ARMY TM 5-818-4AIR FORCE AFM 88-5, Chap. 5

BACKFILLFOR

SUBSURFACE STRUCTURES

D E P A R T M E N T S O F T H E A R M Y A N D T H E A I R F O R C EJUNE 1983

*TM 5-818-4/AFM 88-5, Chap. 5

TECHNICAL MANUAL

No. 5-818-4AIR FORCE MANUAL

NO. 88-5, CHAPTER 5

Number2- l2-22-32-42-57-lB-lB-2

HEADQUARTERSDEPARTMENTS OF THE ARMY

AND THE AIR FORCEWASHINGTON, DC, 1 June 1983

BACKFILL FOR SUBSURFACE STRUCTURES

CHAPTER 1. INTRODUCTIONBackground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2. PLANNING AND DESIGN OF STRUCTURES AND EX-CAVATIONS TO ACCOMMODATE BACKFILL OP-ERATIONS

General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Effect of excavation and structuraI configuration on back-

fill operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Backfill problem areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Optimum cost construction . . . . . . . . . . . . . . . . . . . . . . . . .

3. EVALUATION, DESIGN, AND PROCESSING OF BACK-FILL MATERIALS

General.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Evaluation of backfill materials. . . . . . . . . . . . . . . . . . . . . .Selection of backfill materials . . . . . . . . . . . . . . . . . . . . . . .Processing of backfill materials . . . . . . . . . . . . . . . . . . . . . .

4. EARTHWORK: EXCAVATION AND PREPARATIONFOR FOUNDATIONS

Excavation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Foundationpreparation . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5. BACKFILL OPERATIONSPlacement of backfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Installation of instruments. . . . . . . . . . . . . . . . . . . . . . . . . .Postconstruction distress. . . . . . . . . . . . . . . . . . . . . . . . . . . .

6. SPECIFICATION PROVISIONSGeneral.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Excavation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Foundation preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . .Backfill operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7. CONSTRUCTION CONTROLGeneral.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Corps acceptance control organization. . . . . . . . . . . . . . . . .Excavation control techniques. . . . . . . . . . . . . . . . . . . . . . .Foundation preparation control techniques . . . . . . . . . . . . .Backfill quality acceptance control . . . . . . . . . . . . . . . . . . .

Paragraph Page

l - ll - 2

l - ll - l

2 - l 2 - l

2-2 2 - l2-3 2-42-4 2-92-5 2-9

3 - l 3 - l3-2 3 - l3-3 3-43-4 3-7

4 - l 4 - l4-2 4-2

5 - l5-25-3

5 - l5-45-5

6 - l 6 - l6-2 6 - l6-3 6-2

6-4 6-2

7 - l7-27-37-47-5

7 - l7 - l7-37-37-3A - lAPPENDIX A. REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B. FUNDAMENTALS OF COMPACTION, FIELD COMPACTION TESTMETHODS, AND FIELD MOISTUREDENSITY TEST METHODS . . .

C. BIBLIOGRAPHY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LIST OF FIGURES

Open backfill zonesTitle

Confined backfill zonesComplex structuresExcavation subject to bottom heaveExcess lateral pressure against vertical walls induced by compactionAcceptance rejection scheme for a backfill areaCompaction CurveTypical compaction test curves

B - lC- l

*This manual supersedes TM 5-818-4/AFM 88-5, Chapter 5, 7 June 1969.

i

TM 5-818-4/AFM 88-5, Chap. 5

Number TitleB-3 Molding Water content versus density-lean clay (laboratory impact compaction)B-4 Illustration of one-point compaction methodB-5 Illustration of possible error using one- and two-point compaction methodsB-6 Illustration of two-point compaction methodB-7 Correlation between dry density and hand cone resistance at a depth of 6 inches below the surfaceB-8 Power applied by the oven to dry moist soils

Number3- l5- l

LIST OF TABLESTitle

Typical engineering properties of compacted materialsSummary of compaction criteria

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TM 5-818-4/AFM 88-5, Chap. 5

CHAPTER 1

INTRODUCTION

1-1. Background. Military facilities for theArmy and Air Force have included construction ofbuildings and other structures partially below groundsurface. In more recent years, missile launching andsupport structures, fallout and blast-protection shel-ters, and command-control centers have been con-structed below ground surface. Many of these struc-tures were constructed using cut-and-cover proceduresand required backfilling within confined areas usingvarious types of soil.

a. Numerous deficiencies in backfilling operationsoccurred in some of the earlier missile-launch con-struction programs and caused conditions that jeop-ardized the proper functioning of those structures.Measures to correct deficiencies were both time con-suming and costly. It was recognized that critical areasmust be delineated and the causes of the deficienciesbe determined and corrected.

b. Measures were taken to alleviate the overall back-filling problems. These measures were progressivemodification of design and configuration of structures,more detailed instructions to the construction person-nel, and close control during construction to ensurethat proper construction practices were being fol-lowed.

(1) Some of the problem areas were eliminated bymodification of design and configuration of structuresto allow easier placement of backfill and to permit ac-cess of compaction equipment so that requireddensities could beachieved.

(2) Construction personnel were issued more de-tailed field directives covering some of the particularlydifficult phases of backfill placement.

(3) Inspector training programs were conducted topoint out critical areas and emphasize proper backfillprocedures and the need for continuous surveillanceand close control.

c. The advent of energy efficient structures, partial-ly embedded below ground level, had increased the useof backfill. In addition, the ever increasing need forfuel conservation requires maximum use of all exca-vated or onsite materials for backfill to reduce fuelneeded for hauling in better materials from offsite.Thus, innovative planning and design and good con-struction control using rapid check tests are impera-tive for all backfill operations.

1-2. Purpose and scope. This manual is for theguidance of designers, specification writers, and es-pecially field personnel engaged in designing, plan-ning, and conducting earthwork operations aroundmajor deep-seated or subsurface structures.

a. The greatest deficiencies in earthwork operationsaround deep-seated or subsurface structures occur be-cause of improper backfilling procedures and inade-quate construction control during this phase of thework. Therefore, primary emphasis in this manual ison backfilling procedures. Design and planning con-siderations, evaluation and selection of materials, andother phases of earthwork construction are discussedwhere pertinent to successful backfill operations.

b. Although the information in this manual is pri-marily applicable to backfilling around large and im-portant deep-seated or buried structures, it is also ap-plicable in varying degrees to backfilling operationsaround all structures, including conduits.

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TM 5-818-4/AFM 88-5, Chap. 5

CHAPTER 2

PLANNING AND DESIGN OF STRUCTURES ANDEXCAVATIONS TO ACCOMMODATE BACKFILL OPERATIONS

2-1. General. Many earthwork construction prob-lems can be eliminated or minimized through properdesign, thorough planning, and recognition of problemareas effecting backfill operations. Recognition andconsideration must be given in planning to design fea-tures that will make backfilling operations less diffi-cult to accomplish. Examples of problem areas andhow forethought in design and planning can help toeliminate backfill deficiencies are presented in the fol-lowing paragraphs.

2-2. Effect of excavation and structuralconfiguration on backfill operations.Some of the problems encountered in earthwork con-struction are related to the excavation and the configu-ration of the structures around which backfill is to beplaced. It is the designer’s responsibility to recognizethese problems and to take the necessary measures tominimize their impact on the backfill operations.

a. Open zones. An open zone is defined as a backfillarea of sufficient dimensions to permit the operation

of heavy compaction equipment without endangeringthe integrity of adjacent structures around which com-pacted backfill operations are conducted. Figure 2-1shows examples of open zones. In these zones wherelarge compaction equipment, can operate, it is general-ly not too difficult to obtain the desired density if ap-propriate materials and proper backfill procedures areused. For areas that can be economically compacted byheavy equipment, the designer can avoid problems byincluding in the design provisions sufficient workingspace between structures or between excavation slopesand structures to permit access by the heavy compac-tion equipment. Generally, a working space of at least12 feet between structure walls and excavation slopesand at least 15 feet between structures is necessary forheavy equipment to maneuver. In addition to maneu-vering room, the designer must also consider any ad-verse loading caused by the operation of heavy equip-ment too close to structure walls, as discussed in para-graph 2-3d.

b. Confined zones. Confined zones are defined asareas where backfill operations are restricted to theuse of small mechanical compaction equipment (fig.2-2) either because the working room is limited or be-cause heavy equipment (fig. 2-1) would impose exces-sive soil pressures that could damage the structure.Most deficiencies in compacted backfill around subsur-

face structures have occurred in confined zones whererequired densities are difficult to achieve because ofrestricted working room and relatively low compactioneffort of equipment that is too lightweight. The use ofsmall equipment to achieve required compaction isalso more expensive than heavy equipment since thin-ner lifts are required. However, because small compac-tion equipment can operate in spaces as narrow as 2feet in width, such equipment is necessary to achievethe required densities in some areas of most backfillprojects. Therefore, the designer should plan structureand excavation areas to minimize the use of small com-paction equipment.

c. Structure configuration. The designer familiarwith backfilling operations can avoid many problemsassociated with difficult to reach confined zones,which are created by structural shapes obstructing theplacement and compaction of backfill, by consideringthe impact of structural shape on backfill operations.In most cases, structural shapes and configurationsthat facilitate backfill operations can be used withoutsignificantly affecting the intended use of the struc-ture.

(1) Curved bottom and wall structures. Areas be-low the spring line of circular, elliptical, and similarshaped structures are difficult to compact backfillagainst because compaction equipment cannot get un-der the spring line. If possible, structures should be de-signed with continuously curved walls and flat floorssuch as in an igloo-shaped structure. For structureswhere a curved bottom is required to satisfy the in-tended function, it may be advisable for the designerto specify that a template shaped like the bottom ofthe structure be used to guide the excavation below thespring line so that uniform foundation support will beprovided.

(2) Complex structures. Complex structures havevariable shaped walls and complex configurations inplan and number of levels. These structures can also besimple structures interconnected by access shafts, tun-nels, and utility conduits. Because of their irregularshapes and configurations the different types of struc-tures significantly increase excavation and backfillproblems.

(a) Typical examples of complex structures arestepped multilevel structures and multichamberedstructures with interconnecting corridors (fig. 2-3).Complex structures are generally more difficult to

2 - 1

TM 5-818-4/AFM 88-5, Chap. 5

Figure 2- 1. Open backfill zones.

compact backfill around and are more likely to havesettlement problems (para 2-3a). Although the multi-level step structure (fig. 2-3a) is not particularly diffi-cult to compact backfill around, at least for the firstlevel, the compaction of backfill over the offset struc-ture will generally require the use of small equipment.Small equipment will also be required for compactionof backfill around and over the access corridor and be-tween the two chambers (fig. 2-3b). Where possible,the design should accommodate intended functionsinto structures with uniformly shaped walls and a sim-ple configuration.

(b) Where structures of complex configurationsare necessary, construction of a three-dimensionalmodel during the design and planning phases will beextremely beneficial. From the model, designers canmore easily foresee and eliminate areas in which itwould be difficult to place and compact backfill.

d. Service conduits. Since compaction of backfill isdifficult around pipes and conduits, utility lines should

be grouped together or placed in a single large conduitwhere feasible rather than allowed to form a haphaz-ard maze of pipes and conduits in the backfill. Utilitylines should be run either horizontally or verticallywherever possible. Plans for horizontally run appur-tenances, such as utility lines, access tunnels, andblast-delay tubing, should be coordinated with the ex-cavation plans so that wherever feasible these appur-tenances can be supported by undisturbed soils ratherthan by compacted backfill.

e. Excavation plans. The excavation plans should bedeveloped with the backfill operations and the struc-ture configurations in mind. The excavation and allcompleted structures within the excavation should beconducive to good backfill construction procedures,and access should be provided to all areas so that com-paction equipment best suited to the size of the areacan be used. The plans for excavation should also pro-vide for adequate haul roads and ramps. Positive exca-vation slopes should be required in all types of soil de-

2-2

TM 5-818-4/AFM 88-5, Chap. 5

Figure 2-2. Confined backfield zones.

(a) TWO-STORY STRUCTURE

(b) CONNECTING STRUCTURES

Figure 2-3. Complex structures.

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TM 5-818-4/AFM 88-5, Chap. 5

posits to facilitate compaction of backfill against theslope and to ensure good bond between the backfill andthe excavation slopes. Loose material should be re-moved from the excavation slopes; in some cases,benches may be required to provide a firm surface tocompact backfill against.

f. Lines and grades. Care should be exercised inplanning lines and grades for excavation to ensurethat uniform, adequate support is provided at thefoundation level of important structures. Generally,foundations consisting of part backfill and part undis-turbed materials do not provide uniform bearing andshould be avoided wherever possible. The foundationshould be overexcavated where necessary, and back-filled with compacted select material to provide unif-orm support for the depth required for the particularstructure. Where compacted backfill is required be-neath a structure, the minimum depth specified shouldbe at least 18 inches.

g. Thin- walled metal structures. Thin-walled, corru-gated metal structures are susceptible to deflections ofstructural walls when subjected to backfill loads. Ad-verse deflections can be minimized by planning back-fill operations so that compacted backfill is brought upevenly on both sides of the structure to ensure uniformstress distribution. Temporary surcharge loads appliedto the structure crown may also be required to preventvertical distortions and inward deflection at the sides.

2-3. Backfill problem areas. Other featuresthat have the potential to become problem areas arediscussed in the following paragraphs. These potentialproblem areas have to be considered during the plan-ning and design phases to minimize deficiencies instructure performance associated with backfill place-ment and to make backfilling operations less difficult.

a. Settlement and downdrag. In the construction ofunderground structures and particularly missile-launch-site facilities, tolerances to movement are oftenconsiderably less than those in normal construction.The design engineer must determine and specify allow-able tolerances in differential settlement and ensurethat differential settlement is minimized and/or ac-commodated. Settlement analysis procedures are out-lined in TM 5-818-l/AFM 88-3, Chapter 7. See ap-pendix A, References.

(1) Critical zones. Critical backfill zones are thoseimmediately beneath most structures. Consolidationand swelling characteristics of backfill materialsshould be thoroughly investigated so that materialshaving unfavorable characteristics will not be used inthose zones. Some settlement can be expected to takeplace, but it can be minimized by requiring a higherthan normal compacted density for the backfill. Cohe-sive backfill compacted at a water content as little as 3

2-4

to 4 percentage points below optimum may result inlarge settlements caused by collapse of nonswellingsoil material or heave of swelling materials upon sat-uration after construction. Compacting cohesive back-fill material at optimum water content or slightly onthe wet side of optimum generally will reduce theamount of settlement and swelling that would occur.The reduction should be confirmed by consolidationand swell tests on compacted specimens (para 3-2b(4)).

(2) Service conduits. Settlement within the back-fill around structures will also occur. A proper designwill allow for the estimated settlement as determinedfrom studies of consolidation characteristics of thecompacted backfill. Where service conduits, access cor-ridors, and similar facilities connect to the structureoversize sleeves, flexible connections and other protec-tive measures, as appropriate, may be used to preventdamage within the structure.

(3) Differential settlement. Complex structuresare more susceptible to differential settlement becauseof the potential for large variations in loads carried byeach component foundation. In the multilevel steppedstructure (fig. 2-3a), the foundation supporting thelower level offset component must also support thevolume of backfill over that part of the structure.Measures must be taken to ensure that the properfunctioning of all elements is not hampered by differ-ential settlement. The increased cost of proper designand construction where unusual or difficult construc-tion procedures are required is insignificant whencompared with the cost of the structure. The cost of re-medial measures to correct deficiencies caused by im-proper design and construction usually will be greaterthan the initial cost required to prevent the deficien-cies.

(4) Downdrag. In addition to conventional serviceloads, cut and cover subsurface structures are suscepti-ble to downdrag frictional forces between the struc-ture and the backfill that are caused by settlement ofthe backfill material adjacent to and around the struc-ture. Downdrag loads can be a significant proportionof the total vertical load acting on the structure andmust be considered in the structure settlement analy-sis. Structure-backfill friction forces may also generatesignificant shear forces along the outer surface ofstructures with curve-shaped roofs and walls. Themagnitude of the friction forces depends upon the typeof backfill, roughness of the structure’s surface, andmagnitude of earth pressures acting against the struc-ture. Techniques for minimizing downdrag frictionforces generally include methods that reduce the struc-ture surface roughness such as coating the structure’souter surface with asphalt or sandwiching a layer ofpolyethylene sheeting between the structure’s outersurface and fiberboard (blackboard) panels. Backfillsettlement and associated downdrag can also be mini-

TM 5-818-4/AFM 88-5, Chap. 5

Figure 2-4. Excavation subject to bottom heave.

mized by requiring higher backfill densities adjacentto the structure.

mized by adequate planning and implementation ofgroundwater investigations.

b. Groundwater. Groundwater is an importantconsideration in planning for construction of subsur-face structures. If seepage of groundwater into the ex-cavation is not adequately controlled, backfillingoperations will be extremely difficult. The ground-water level must be lowered sufficiently (at least 2 to 3feet for granular soils and as much as 5 to 10 feet forfine-grained soils below the lowest level of backfilling)so that a firm foundation for backfill can be estab-lished. If the level is not lowered, the movement ofhauling or compaction equipment may pump seepagewater through the backfill, or the initial backfill layersmay be difficult to compact because of an unstablefoundation. Since the proper water content of thebackfill is essential for achieving proper compaction,prevention of groundwater seepage into the excava-tion during backfilling operations is mandatory.Figure 3-14 of EM 1110-2-1911 shows a method fordewatering rock foundations.

(1) The contractor is generally responsible for thedesign, installation, and operation of dewateringequipment. The Corps of Engineers is responsible forspecifying the type of dewatering system and evaluat-ing the contractor’s proposed dewatering plan. Sincethe dual responsibility of the contractor and the Corpsrelies on a thorough understanding of groundwaterconditions, inadequate dewatering efforts can be mini-

(2) The possibility of hydraulic heave in cohesivematerial must also be investigated to ensure stabilityof the excavation floor. Hydraulic heave may occurwhere an excavation overlies a confined permeablestratum below the groundwater table (fig. 2-4). If theupward hydrostatic pressure acting at the bottom ofthe confining layer exceeds the weight of overburdenbetween the bottom of the excavation and the confin-ing layer, the bottom of the excavation will rise bodilyeven though the design of the dewatering system isadequate for control of groundwater into the excava-tion. To prevent heave, the hydrostatic pressure be-neath the confined stratum must be relieved.

(3) Subsurface structures located in part or whollybelow the groundwater table require permanent pro-tection against groundwater seepage. The type of pro-tection may range from simple impermeable barriersto complex permanent dewatering systems.

(4) Dewatering and groundwater control proce-dures are described in TM 5-818-5/NACFACP-418/AFM 88-5, Chapter 6.

c. Gradation and filter criteria for drainage materi-als. Groundwater control is often accomplished byditches positioned to intercept the flow of groundwa-ter and filled with permeable granular material. Thewater is generally collected in perforated pipes locatedat the bottom of the ditch and pumped to a suitable

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TM 5-818-4/AFM 88-5, Chap. 5

discharge area. Such drainage systems are referred toas filter drains. The gradation of the granular filtermaterial is critical for the functioning of the system.Selection of the proper gradation for the filter materi-al is dependent upon the gradation of the material thatis being drained. Drainage of silts and clays usually re-quires a graded filter made up of several layers ofgranular material with each layer having specific re-quirements for maximum grain size and gradation. De-tails on the design of filter drains are presented in TM5-818-5/NAVFACP-418/AFM 88-5, Chapter 6.

(1) Selected material. If materials at the jobsite donot meet the designed filter requirements, select ma-terial must be purchased from commercial sources andshipped to the jobsite. Filter material must be stock-piled according to gradation. For graded filter sys-tems, the materials must be placed with care to mini-mize mixing of individual components.

(2) Filter cloths. Both woven and nonwoven filtercloths, which have been found satisfactory for use as afilter media for subsurface drains, are available. Whengranular filter materials are not economicallyavailable, a single wrap of filter cloth around a pipemay be used in lieu of a coarser backfill. Whenavailable granular filter material is too coarse to satis-fy filter criteria for the protected soil, a single layer offilter cloth may be used adjacent to the protected soil.To reduce the chance of clogging, no filter cloth shouldbe specified with an open area less than 4 percent andor equivalent opening size (EOS) of less than the No.100 sieve (0.0059 inch). A cloth with openings as largeas allowable should be specified to permit drainageand prevent clogging. Additional information on air-field drainage is contained in TM 5-820-2/AFM 88-5,Chapter 2.

(3) Other uses. Filter cloth can also provide pro-tection for excavated slopes and serve as a filter to pre-vent piping of fine-grained soils. In one project, sandwas not available for backfill behind a wall and coarsegravel had to be used to collect seepage. The filtercloth used to protect the excavated slope served as afilter against piping of the natural silty clay underseepage gradients out of the excavated slope after thecoarse gravel backfill was placed.

d. Earth pressures. The rationale design of anystructure requires the designer to consider all loadsacting on the structure. In addition to normal earthpressures associated with the effective pressure dis-tribution of the backfill materials, subsurface cut-and-cover structures may also be subjected to surchargeloads caused by heavy equipment operating close tothe structure and by increased permanent lateral earthpressures caused by compaction of backfill materialwith heavy equipment. Procedures for predicting nor-mal earth pressures associated with the effective pres-sure of backfill materials are discussed in TM

2-6

5-818-1/AFM 88-3, Chapter 7, EM 1110-2-2902,and EM 1110-2-2502.

(1) Exact solutions for surcharge earth pressuresgenerated by heavy equipment (or other surchargeloads) do not exist. However, approximations can bemade using appropriate theories of elasticity such asBoussinesq’s equations for load areas of regular shapeor Newmark’s charts for irregular shaped load areas asgiven in NAVFAC DM-7. As a conservative guide,heavy-equipment surcharge earth pressures may beminimized by specifying that heavy compaction equip-ment maintain a horizontal distance from the struc-ture equivalent to the height of the backfill above thestructure’s foundation.

(2) Compaction-induced earth pressures can causea significant increase in the permanent lateral earthpressures acting on a vertical wall of a structure (fig.2-5a). This diagram is based on the assumption thatthe equipment can operate to within 6 inches of thewall. Significant reductions in lateral pressures occuras the closest allowable distance to the wall is in-creased (fig. 2-5b). For an operating distance 5 feetfrom the wall, the induced horizontal earth pressure ismuch less than that caused by the backfill. The magni-tude of the increase in lateral pressure is dependent,among other factors, on the effective weight of thecompaction equipment and the weight, earth pressurecoefficient, and Poisson’s ratio of the backfill material.Compaction-induced earth pressures against walls arealso described in TM 5-818-l/AFM 88-3, Chapter 7,and EM 1110-2-2502.

(3) The designer must evaluate the economics ofthe extra cost of structures designed to withstand veryclose-in operation of heavy compaction equipmentversus the extra cost associated with obtaining re-quired compaction of backfill in thin lifts with smallercompaction equipment. A more economical alternativemight be to specify how close to the walls differentweights of compaction equipment can be operated.

(4) One method of reducing lateral earth pres-sures behind walls has been to use about 4 feet of un-compacted granular (sand or gravel) backfill above thebase of the wall. Soil backfill can then be compacted inlayers above the granular backfill. Compression of thegranular material prevents the buildup of excessivelateral pressures against the wall.

e. Structural backfill. Structural backfill is definedas the compacted backfill required over and around astructure to prevent damage from heavy equipmentoperating over or near the structure. This backfillmust be compacted using small compaction equip-ment, such as mechanical rammers or vibratory-platecompactors, or intermediate size equipment such aswalk-behind, dual-drum vibratory rollers. The hori-zontal and vertical distances from the structure forwhich structural backfill is required should be deter-

TM 5-818-4/AFM 88-5, Chap. 5

a. MAXIMUM INDUCED LATERAL PRESSURES

b. EFFECT OF DISTANCE FROM WALL

Figure 2-5. Excess lateral pressure against vertical walls induced by compaction.

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TM 5-818-4/AFM 88-5, Chap. 5

mined from estimates of loads acting on the structurecaused by heavy equipment and on the strength of theembedded structure members as discussed in d above.A 2-foot cover over small utility conduits and pipes isadequate protection where proper bedding proceduresare followed. The minimum cover requirements overlarger diameter (6 inches or greater), rapid and flexiblepipes are presented in appendix II of TM 5-820-4/AFM 88-5, Chapter 4.

f. Slopes and bracing. Where open excavation isplanned, consideration should be given to the slopes towhich the materials to be encountered can be cut andremain stable. The stability analysis should includethe strength of the materials, groundwater conditions,and any surcharge load that may be imposed as the re-sult of stockpiles being placed or equipment operatingnear the crest of the excavation. Slope stability evalua-tion procedures are described in TM 5-818-1/AFM88-3, Chapter 7. Shoring and bracing should be usedto support excavation slopes where it is not feasible toexcavate to stable slopes (TM 5-818-l/AFM 88-3,Chapter 7). Requirements for shoring and bracingsafety are presented in EM 385-l-l.

g. Bedding for curved-bottom structures. Founda-tions for pipes, conduits, access tunnels, fuel and wa-ter storage tanks, and other curved-bottom structuresconstructed within the backfill are considered criticalzones that require special attention. Any bedding ma-terial used should be free of stones or other large parti-cles that would lead to nonuniform bearing. One of themost important functions of any bedding procedure isto provide firm support along the full length of thestructure. For areas where it is difficult to performfield density control tests because of limited workingspace, a procedure to ensure that proper compaction isobtained must be employed. Several methods of ob-taining adequate bedding are discussed in paragraph5-1c (2).

h. Cold weather construction. Cold weather canhave a very adverse effect on backfilling operationsand can cause considerable delay. If possible, the proj-ect should be planned to complete backfilling opera-tions prior to any extended period of freezing tempera-tures. The contractor and the resident engineer mustkeep up to date with weather data so that the con-tractor can plan the equipment and construction forcerequired to meet the construction schedule and to pro-tect the work already accomplished.

(1) The designer must establish definite limita-tions and requirements regarding placement of back-fill when the ambient temperature is below freezing.Most inorganic soils, particularly silts and lean clays,containing 3 percent, by weight, or more of particlesfiner than 0.02 millimetre in diameter are frost sus-ceptible. Such soils, when frozen in the presence of an

2-8

available source of water, develop segregated ice in theform of lenses, layers, veins, or masses commonly, butnot always oriented normal to the direction of heatloss. The expansion of the soil mass resulting from icesegregation is called frost heave. Frost heave of soilunder and against structures can cause detrimental ef-fects, which can be compounded during subsequentthawing by differential movement, loss of density, andloss of shear strength. Soils of this type should not beplaced during or immediately prior to freezingtemperatures and must not be placed in critical areas.Nonfrost susceptible soils should be used at thefinished grade to the depth of frost penetration whenthe finished grade serves as a load-bearing surface.

(2) Additives, such as calcium chloride, can beused to lower the freezing temperature of soil water,but such additives will ordinarily also change the com-paction and water content requirements. Therefore,additives must not be used without prior investigationto determine their effect on compaction and water con-tent requirements. Dry sand or sand-gravel mixturescan be placed satisfactorily when temperatures are be-low freezing without serious effects.

(3) Protection must be provided for in-placepermanent backfill in critical areas, such as thosearound and under structures and embedded items al-ready placed. To preclude structural damage from pos-sible frost heave, backfill materials around such struc-tures should be insulated with a protective covering ofmulch, hay, or straw. In some instances, loose lifts ofsoil can be used for insulation. However, rock or sandis too porous to provide sufficient insulation and toopermeable to resist water penetration. If soil is to beused as an insulating material, a material completelyforeign to the permanent fill, such as straw or buildingpaper, should be laid down prior to placement of theinsulation fill so that there will be a marked distinc-tion between the permanent and the temporary insula-tion fills. In this way, when the insulation fill is re-moved, the stripping limits can be readily discerned.

(4) Flooding of the excavation has also been usedsuccessfully to prevent frost penetration of the in-place permanent backfill. However, considerationmust be given to possible detrimental effects ofsaturating in-place backfill and the delay of removingthe water at the beginning of the next constructionseason if it freezes into a solid mass of ice.

(5) Concrete walls and floors of completed struc-tures provide poor insulation for the fill around andbeneath these structures. Therefore, these structuresshould be enclosed as much as possible and kept closedduring the winter when construction is halted becauseof adverse freezing weather. Reinforcing steel protrud-ing from a partially completed structure will conductcold through the concrete and increase the rate anddepth of frost penetration beneath the structure.

Every effort should be made to schedule constructionso that this condition will be kept to a minimum, andprotection must be required where necessary.

i. Seismic zones. The design considerations for sub-surface structures subjected to dynamic loads causedby seismic activity or explosive devices are beyond thescope of this manual. Design details are provided inTM 5-818-1/AFM 88-3, Chapter 7, and ER1110-2-1806. Specific problems relating to backfilloperations are primarily limited to possible potentialfor dynamically induced liquefaction. Certain materi-als are particularly susceptible to liquefaction; theseinclude saturated gravels, sands, silts, and clayeysands and gravel. Where these materials are used asbackfill, the potential for liquefaction can be mini-mized by requiring a high degree of compaction,particularly in critical areas such as beneath footingsand under the spring line of curved wall structures.The requirements for materials susceptible to liquefac-tion are discussed in paragraph 3 - 3d.

2-4. Instrumentation. For important struc-tures of unique design or for structures where the po-tential for postconstruction distress exists, instrumen-tation of the structure should be considered. The in-strumentation program may include monitoring theamount and rate of settlement, movement of retainingwalls and other structural elements, development ofstresses within the structure, and development of hy-drostatic and earth pressures against the structure.Analysis of the data will furnish a check on design as-sumptions and indicate what measures must be takento relieve or correct undesirable conditions beforedistress develops. Information of this nature can alsobe of significant value in future design and construc-tion.

a. Requirements. Specific requirements for instru-ments are ruggedness, reliability over the projectedservice life, and simplicity of construction, installa-tion, and observation. Other important considerationsin selecting the type of instruments are cost andavailability. Manufacturers of devices considered forinstallation should be asked to provide a list of projectson which their devices have been installed, and previ-ous users of new equipment should be contacted to as-certain their operating experiences.

b. Installation and observation of instrumentation.A rational instrumentation program must use theproper type of instruments and have the instrumentsinstalled properly at critical locations. Valid readingsoften depend on techniques and procedures used in in-stalling and observing the instrumentation.

(1) Schedules for observations are generally estab-lished by the design office. Initial observations shouldbe checked to assure their validity and accuracy, since

TM 5-818-4/AFM 88-5, Chap. 5

these readings usually form the basis to which subse-quent observations are related. Observations should beplotted immediately after each set of readings is takenand evaluated for reasonableness against previous setsof readings. In this way, it is often possible to detecterrors in readings and to obtain check readings beforesignificant changes in field conditions occur.

(2) EM 1110-2-1908 discusses in detail varioustypes of instrumentation devices; procedures for in-stallation, observation, and maintenance; collection,recording, analysis, and reporting of data; and possiblesource of error and causes of malfunctions.

2-5. Optimum cost construction. The de-signer should consider all details of the constructionprocess to ensure a safe and operational facility at thelowest possible cost.

a. Energy requirements. The consideration of ener-gy requirements is important not only for economicalreasons but also for the critical need to conserve ener-gy wherever possible. It should not be the intent of thedesign engineer to unduly restrict the competitive na-ture of current contractural procedures. Nevertheless,there are certain alternatives that the designer mayspecify that potentially could lead to more energy effi-cient construction with cost saving being reflected inbid prices. Some of the possible alternatives thatshould be considered are discussed below.

(1) Sources of suitable select backfill materialshould be located as close to the project site as possi-ble. The source may be either a borrow area or a com-mercial vendor.

(2) Hauling routes to and from the source of back-fill and the project site should follow the most directroute.

(3) Only compaction equipment that will compactthe specific backfill to the required density in an effi-cient manner should be approved for use. For largeprojects, the designer may require that the contractordemonstrate the capabilities of the equipment he in-tends to use prior to construction.

(4) If possible, material from excavations or with-in the immediate vicinity of the project site should beused as backfill, even though such material may bemarginally suitable. The engineering characteristics ofmarginal material may be enhanced by the use of addi-tives (para 3-3d).

(5) The energy requirements for adequate coldweather protection of construction personnel andstructures can be considerable. For project sites sub-ject to seasonal cold weather, construction should not,if possible, be scheduled during extreme cold weatherperiods.

b. Value engineering. Potential cost savings may berealized by encouraging the contractor to participatein value engineering, whereby the contractor shares

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TM 5-818-4/AFM 88-5, Chap. 5

any project saving derived from realistic cost-savingsuggestions submitted.

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TM 5-818-4/AFM 88-5, Chap. 5

CHAPTER 3

EVALUATION, DESIGN, AND PROCESSINGOF BACKFILL MATERIALS

3-1. General. The evaluation, design, and properprocessing of backfill materials are extremely impor-tant phases of the preconstruction operations. Thepurpose of the evaluation phase is to determine the en-gineering characteristics of potential backfill materi-als. The design phase must take into account the engi-neering characteristics required of the backfill andspecify materials that, when compacted properly, willhave these characteristics. Proper processing of thebackfill material will ensure that desirable engineering.characteristics will be obtained as the material isplaced.

3-2. Evaluation of backfill materlals.Evaluation of backfill materials consists of explora-tion, sampling, and laboratory testing to determinethe engineering characteristics of potential backfillmaterials. Detailed instructions for exploration, sam-pling, laboratory testing, and foundation design arepresented in TM 5-818-1/AFM 88-3, Chapter 7. How-ever, to emphasize the need for an adequate investiga-tion, some aspects of planning and investigation thatshould be considered are discussed in the followingparagraphs.

a. Field exploration and sampling. Field explorationand sampling are extremely important to the design offoundations, selection of backfill, and planning forconstruction. A great amount of material will be avail-able from required excavations, and the investigationfor foundation conditions should include the samplingand evaluation of these materials for possible use asbackfill. Where an adequate volume of suitable back-fill cannot be obtained from the construction excava-tion, the exploration and sampling program must beexpanded to find other sources of suitable materialwhether from nearby borrow areas or commercialsources.

(1) The purpose of the investigation is to delineatecritical conditions and provide detailed information onthe subsurface deposits so that proper design and con-struction, including backfilling operations, can be ac-complished with minimum difficulty. Thus carefulplanning is required prior to the field exploration andsampling phase of the investigation. Available geo-logic and soil data should be studied, and if possible,preliminary borings should be made. Once a site hasbeen tentatively selected, orientation of the structureto the site should be established. The engineer who

plans the detailed field exploration program musthave knowledge of the structure, i.e., its configurationand foundation requirements for design loads and set-tlement tolerances. The planning engineer should alsoknow the type and quantity of backfill required. Theimportance of employing qualified field explorationpersonnel cannot be overemphasized. The explorationcrews should be supervised in the field by a soils engi-neer or geologist familiar with the foundation andbackfill requirements so that changes can be made inthe exploration program where necessary to provideadequate information on subsurface conditions.

(2) The field engineer should also know the loca-tion of significant features of the structure so thatsampling can be concentrated at these locations. In ad-dition, he should have an understanding of the engi-neering characteristics of subsurface soil and rock de-posits that are important to the design of the structureand a general knowledge of the testing program sothat the proper type and quantity of samples will beobtained for testing.

(3) From the samples, the subsurface deposits canbe classified and boring logs prepared. The more con-tinuous the sampling operation, the more accurate willbe the boring logs. All borings should be logged withthe description of the various strata encountered asdiscussed in TM 5-818-1/AFM 88-3, Chapter 7. Accu-rate logging and correct evaluation of all pertinent in-formation are essential for a true concept of subsur-face conditions.

(4) When the exploratory borings at the construc-tion site have been completed, the samples and logs ofborings should be examined to determine if the materi-al to be excavated will be satisfactory and in sufficientquantity to meet backfill requirements. Every effortshould be made to use the excavated materials; how-ever, if the excavated materials are not satisfactory orare of insufficient quantity, additional explorationshould be initiated to locate suitable borrow areas. Ifborrow areas are not available, convenient commercialsources of suitable material should be found. Backfillsources, whether excavation, borrow, or commercial,should contain several times the required volume ofcompacted backfill.

(5) Groundwater studies prior to construction ofsubsurface structures are of the utmost importance,since groundwater control is necessary to provide adry excavation in which construction and backfilling

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TM 5-818-4/AFM 88-5, Chap. 5

operations can be properly conducted. Data on ground-water conditions are also essential for forecasting con-struction dewatering requirements and stability prob-lems. Groundwater studies must consist of investiga-tions to determine: groundwater levels to include anyseasonal variations and artesian conditions; the loca-tion of any water-bearing strata; and the permeabilityand flow characteristics of water-bearing strata. Meth-ods for investigating groundwater conditions are de-scribed in TM 5-818-1/AFM 88-3, Chapter 7, and TM5-818-5/NAVFACP-418/AFM 88-5, Chapter 6.

b. Laboratory testing. The design of any foundationis dependent on the engineering characteristics of thesupporting media, which may be soil or rock in eitherits natural state or as compacted backfill. The labora-tory testing program will furnish the engineer infor-mation for planning, designing, and constructing subsurface structures. Laboratory testing programs usual-ly follow a general pattern and to some extent can bestandardized, but they should be adapted to particularproblems and soil conditions. Special tests and re-search should be utilized when necessary to developneeded information. The testing program should bewell planned with the engineering features of thestructure and backfill in mind; testing should be con-centrated on samples from areas where significant fea-tures will be located but should still present a completepicture of the soil and rock properties. The laboratorytest procedures and equipment are described in TM5-818-1/AFM 88-3, Chapter 7, EM 1110-2-1906,and MIL-STD-621.

(1) Identification and classification of soils. TheUnified Soil Classification System used for classifyingsoils for military projects (MIL-STD-619 and TM5-818-1/AFM 88-3, Chap. 7) is a means of identifyinga soil and placing it in a category of distinctive engi-neering properties. Table 3-1 shows the properties ofsoil groups pertinent to backfill and foundations.Using these characteristics, the engineer can preparepreliminary designs based on classification and planthe laboratory testing program intelligently and eco-nomically.

(a) The Unified Soil Classification System clas-sifies soils according to their grain-size distributionand plasticity characteristics and groups them with re-spect to their engineering behavior. With experience,the plasticity and gradation properties can be esti-mated using simple, expedient tests (see table 2-2 and2-3 of TM 5-818-1/AFM 88-3, Chap. 7 or AFM 89-3,Chap. 2) and these estimates can be confirmed usingsimple laboratory tests. The principal laboratory testsperformed for classification are grain-size analysesand Atterberg limits.

(b) The engineering properties in table 3-1 arebased on “Standard Proctor” (CE 25) maximum

3-2

density except that the California Bearing Ratio (CBR)and the subgrade modulus are based on CE 55 maxi-mum density. This information can be used for initialdesign studies. However, for final design of importantstructures, laboratory tests are required to determineactual performance characteristics, such as CE 55compaction properties, shear strength, permeability,compressibility, swelling characteristics, and frost sus-ceptibility where applicable, under expected construc-tion conditions.

(c) The Unified Soil Classification System isparticularly useful in evaluating, by visual examina-tion, the suitability of potential borrow materials foruse as compacted backfill. Proficiency in visual clas-sification can be developed through practice by com-paring estimated soil properties with results of labora-tory classification tests.

(2) Compaction testing. Compaction test proce-dures are described in detail in MIL-STD-621 andASTM D 1557 (app. A). It is important that the de-signer and field inspection personnel understand thebasic principles and fundamentals of soil compaction.The principles of soil compaction are discussed in ap-pendix B of this manual.

(a) The purpose of the laboratory compactiontests are to determine the compaction characteristicsof available backfill materials. Also, anticipated fielddensity and water content can be approximated in laboratory-compacted samples in order that other engi-neering properties, such as shear strength, compressi-bility, consolidation, and swelling, can be studied. Formost soils there is an optimum water content at whicha maximum density is obtained with a particular com-paction effort. A standard five-point compaction curverelating density and water content (fig. B-1, app. B)can be developed by the procedures outlined in MIL-STD-621.

(b) The impact compaction test results normallyconstitute the basis on which field compaction controlcriteria are developed for inclusion in the specifica-tions. However, for some cohesionless soils, higherdensities can be obtained by the vibratory compactionmethod (commonly referred to as maximum relativedensity), described in appendix XII of EM 1110-2-1906. The required field compaction is generally speci-fied as a percentage of laboratory maximum dry densi-ty and referred to as percent CE 55 maximum density.Water content is an important controlling factor in ob-taining proper compaction. The required percentage ofmaximum dry density and the compaction water con-tent should be selected on the basis of the engineeringcharacteristics, such as compression moduli, settle-ment, and shear strength, desired in the compactedbackfill. It should be noted that these characteristicscould be adversely effected by subsequent increases in

TM 5-818-4/AFM 88-5, Chap. 5

(3) Shear strength testing. When backfill is to beplaced behind structure walls or bulkheads or asfoundation support for a structure, and when fills areto be placed with unrestrained slopes, shear. testsshould be performed on representative samples of thebackfill materials compacted to expected field densi-ties and water contents to estimate as-constructedshear strengths. The appropriate type of test requiredfor the conditions to be analyzed is presented in TM5-818-1/AFM 88-3, Chapter 7. Procedures for shearstrength testing are described in EM 1110-2-1906.

water content after placement. This situation could re-sult from an increase in the groundwater level afterconstruction.

(c) Density control of placed backfill in the fieldcan be facilitated by the use of rapid compaction checktests (para 7-5c). A direct rapid test is the one-pointimpact compaction test. Rapid indirect tests, such asthe Proctor needle penetration for cohesive soils or thecone resistance load for cohesionless soils, can also beused when correlations with CE 55 maximum densityhave been established.

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TM 5-818-4/AFM 88-5, Chap. 5

(4) Consolidation and swell testing. The rate andmagnitude of consolidation under a given load are in-fluenced primarily by the density and type of soil andthe conditions of saturation and drainage. Fine-grained soils generally consolidate more and at aslower rate than coarse-grained soils. However, poorlygraded, granular soils and granular soils composed ofrounded particles will often consolidate significantlyunder load but usually at a relatively fast rate.

(a) The procedure for the consolidation test isoutlined in EM 1110-2-1906. The information ob-tained in this test can be used in settlement analyses todetermine the total settlement, the time rate of settle-ment, and the differential settlement under varyingloading conditions. Consolidation characteristics areimportant considerations in selection of backfill mate-rials. The results of consolidation tests performed onlaboratory compacted specimens of backfill materialcan be used in determining the percent compaction tobe required in the specifications.

(b) Swelling characteristics can be determinedby a modified consolidation test procedure. The degreeof swelling and swelling pressure should be deter-mined on all backfill and foundation materials sus-pected of having swelling characteristics. This fact isparticularly important when a considerable overbur-den load is removed by excavation or when the com-pacted backfill with swelling tendencies may becomesaturated upon removal of the dewatering system andsubsequent rise of the groundwater level. The resultsof swelling tests can be used to determine the suitabil-ity of material as backfill. When it is necessary to usebackfill materials that have a tendency to swell uponsaturation because more suitable materials are un-available, the placement water content and densitythat will minimize swelling can be determined from aseries of tests. TM 5-818-1/AFM 88-3, Chapter 7,and FHWA-RD-79-51 (app. A) provide further infor-mation applicable to compacted backfills.

(5) Permeability tests. Permeability tests to deter-mine the rate of flow of water through a material canbe conducted in the laboratory by procedures describedin EM 1110-2-1906. Permeability characteristics offine-grained materials at various densities can also bedetermined from consolidation tests.

(a) Permeability characteristics for the designof permanent drainage systems for structures foundedbelow the groundwater level must be obtained fromlaboratory tests. The tests should be performed on rep-resentative specimens of backfill materials compactedin the laboratory to densities expected in the field.

(b) In situ material permeability characteristicsfor the design of construction excavation dewateringsystems can also be approximated from laboratorytests on representative undisturbed samples. Labora-tory permeability tests on undisturbed samples are

3-4

less expensive than in situ pumping tests performed inthe field; however, laboratory tests are less accurate inpredicting flow characteristics.

(6) Slake durability of shales. Some clay shalestend to slake when exposed to air and water and mustbe protected immediately after they are exposed. Theextent of slaking also governs the manner in whichthey are treated as a backfill material (para 3-3c).Slaking characteristics can be evaluated by laboratoryjar-slake tests or slake-durability tests.

(a) The jar-slake test is qualitative with six de-scriptive degrees of slaking determined from visualobservation of ovendried samples soaked in tap waterfor as long as 24 hours. The jar-slake test is not astandardized test. One version of the jar-slake test isdiscussed in FHWA-RD-78-141. Six suggested valuesof the jar-slake index are listed below:

Behavior

1 Degrades into pile of flakes or mud2 Breaks rapidly and forms many chips3 Breaks rapidly and forms few chips4 Breaks slowly and forms several fractures5 Breaks slowly and develops few fractures6 No change

Shales with values of 1 to 3 should be protectedwhen occurring in excavated slopes and compacted assoil if used for backfill.

(b) The slake-durability test is a standardizedtest that gives a quantitative description in percent byweight of material remaining intact at the conclusionof the test. Details of the test are presented inFHWA-RD-78-141.

(7) Dynamic tests for special projects. The dynam-ic analysis of projects subject to seismic or blast in-duced loading conditions requires special dynamictests on both in situ and backfill materials. Tests re-quired for dynamic analysis include: cyclic triaxialtests; in situ density measurements; and tests to deter-mine shear wave velocities, shear modulus, and damping (ER 1110-2-1806).

(8) In situ water content. The in situ water con-tent, including any seasonal variation, must be deter-mined prior to construction for materials selected foruse as backfill. Natural in situ water contents will de-termine the need for wetting or drying the backfillmaterial before placement to obtain near optimum wa-ter contents for placement and compaction. ASTM D2216 discusses the test method for determining watercontent.

3-3. Selection of backfill materials. Selec-tion of backfill materials should be based upon theengineering properties and compaction characteristicsof the materials available. The results of the field ex-ploration and laboratory test programs should provideadequate information for this purpose. The materials

may come from required excavation, adjacent borrowpits, or commercial sources. In selecting materials tobe used, first consideration should be given to themaximum use of materials from required excavation.If the excavated materials are deficient in quality orquantity, other sources should be considered. Commonbackfill having the desired properties may be found inborrow areas convenient to the site, but it may be nec-essary to obtain select backfill materials having par-ticular gradation requirements, such as filter sandsand gravels and pipe or conduit bedding materialsfrom commercial sources.

a. Primary considerations. Primary considerationsfor borrow material sources are suitability and quan-tity. Accessibility and proximity of the borrow area tothe jobsite should also be considered. The water con-tents of the borrow area material should be deter-mined seasonally, and a source of water should be lo-cated if the natural water contents are considerablyless than the required placement water content. If sev-eral sources of suitable backfill are available, other fac-tors to be considered in selecting the borrow materialsare ease of loading and spreading and the means foradding or reducing water. The need for separating ormixing soil strata from excavation or borrow sourcesshould be considered if necessary to provide reason-ably uniform engineering properties throughout thecompacted backfill.

b. Compaction characteristics. If compaction char-acteristics of the major portion of the backfill are rela-tively uniform, problems of controlling placement ofbackfill will be significantly reduced since the in-spector will be able to develop more rapidly the abilityto recognize the adequacy of the compaction proce-dures. In addition, the frequency of testing for com-paction control could be reduced. When available back-fill materials are unusual, test sections of compactedbackfill are sometimes justified to develop placementprocedures and to determine the engineering char-acteristics to be expected in field-compacted materials.

c. Workability. An important factor in choosingbackfill materials is the workability or ease with whichthe soil can be placed and compacted. Material charac-teristics that effect workability include: the ease ofadjusting water contents in the field by wetting oraeration; the sensitivity to the compaction water con-tent with respect to optimum; and the amount of com-paction effort required to achieve specified densities.

d. Types of backfill material. A discussion of themany types of backfill and their compaction character-istics is beyond the scope of this manual since soiltypes will vary on each project. However, the compac-tion characteristics of several rather broad categoriesof backfill (table 3-1) are discussed briefly. MIL-

TM 5-818-4/AFM 88-5, Chap. 5

STD-619 should be studied for more detailed informa-tion.

(1) Coarse-grained soils. Coarse-grained soilsinclude gravelly and sandy soils and range from clayeysands (SC) through the well-graded gravels of gravel-sand mixtures (GW) with little or no fines (table 3-l).They will exhibit slight to no plasticity. All of the well-graded soils falling in this category have fairly goodcompaction characteristics and when adequately com-pacted provide good backfill and foundation support.

(a) One difficulty that might arise with soils inthis category would be in obtaining good compactionof the poorly graded sands and gravels. These poorlygraded materials may require saturation with down-ward drainage and compaction with greater compac-tion effort to achieve sufficiently high densities. Also,close control of water content is required where silt ispresent in substantial amounts. Coarse-grained mate-rials compacted to a low relative density are suscepti-ble upon saturation to liquefaction under dynamicloads.

(b) For sands and gravelly sands with little or nofines, good compaction can be achieved in either theair-dried or saturated condition. Downward drainageis required to maintain seepage forces in a downwarddirection if saturation is used to aid in compaction.Consideration may be given to the economy of addingcement to stabilize moist clean sands that are particu-larly difficult to compact in narrow confined areas.However, the addition of cement may produce zoneswith greater rigidity than untreated adjacent backfilland form “hard spots” resulting in nonuniformstresses and deformations in the structure.

(c) Cohesionless materials are well suited forplacement in confined areas adjacent to and aroundstructures where heavy equipment is not permittedand beneath and around irregulary shaped structures,such as tunnels, culverts, utilities, and tanks. Clean,granular, well-graded materials having a maximumsize of 1 inch with 95 percent passing the No. 4 sieveand 5 percent or less passing the No. 200 sieve are ex-cellent for use in these zones. However, a danger existsof creating zones where seepage water may accumulateand saturate adjacent cohesive soils resulting in unde-sirable consolidation or swelling. In such cases, provi-sions for draining the granular backfill, sealing thesurface, and draining surface water away from thestructure are necessary.

(2) Fine-grained soils of low to medium plasticity.Inorganic clays (CL) of low to medium plasticity (grav-elly, sandy, or silty clays and lean clays) and inorganicsilts and very fine sands (ML) of low plasticity (silty orclayey fine sands and clayey silts) are included in thiscategory. The inorganic clays are relatively imperviousand can be compacted fairly easily with heavy compac-

3-5

TM 5-818-4/AFM 88-5, Chap. 5

tion equipment to provide a good stable backfill. Soilsin the CL group can be compacted in confined areas toa fairly high degree of compaction with proper watercontent and lift thickness control. The clayey sands ofthe SC group and clayey silts of the ML group can becompacted to fairly high densities, but close control ofwater content is essential and sometimes critical, par-ticularly on the wet side of optimum water content.Some ML soils, if compacted on the dry side of opti-mum, may lose considerable strength upon saturationafter compaction. Considerable settlement may occur.Caution must therefore be exercised in the use of suchsoils as backfill, particularly below the groundwaterlevel. Also, saturated ML soils are likely to be highlysusceptible to liquefaction when dynamically loaded.Where such soils are used as backfill in seismic proneareas, laboratory tests should be conducted to deter-mine their liquefaction potential (see para. 17-5 and17-6, TM 5-818-1/AFM 88-3, Chap. 7).

(3) Rock. The suitability of rock as backfill mate-rial is highly dependent upon the gradation and hard-ness of the rock particles. The quantity of hard rockexcavated at most subsurface structure sites is rela-tively small, but select cohesionless materials may bedifficult to find or may be expensive. Therefore, exca-vated hard rock may be specified for crusher process-ing and used as select cohesionless material.

(4) Shale. Although shale is commonly referred toas rock, the tendency of some shales to breakdownunder heavy compaction equipment and slake whenexposed to air or water after placement warrants spe-cial consideration.

(a) Some soft shales break down under heavycompaction equipment causing the material to haveentirely different properties after compaction than ithad before compaction. This fact should be recognizedbefore this type of material is used for backfill. Estab-lishing the proper compaction criteria may requirethat the contractor construct a test fill and vary thewater content, lift thickness, and number of coverageswith the equipment proposed for use in the backfilloperation. This type of backfill can be used only inunrestricted open zones where heavy towed or self-pro-pelled equipment can operate.

(b) Some shales have a tendency to break downor slake when exposed to air. Other shales that appearrock-like when excavated will soften or slake and dete-riorate upon wetting after placement as rockfill. Alter-nate cycles of wetting and drying increases the slakingprocess. The extent of material breakdown determinesthe manner in which it is treated as a backfill material.If the material completely degrades into constituentparticles or small chips and flakes, it must be treatedas a soil-like material with property characteristicssimilar to ML, CL, or CH materials, depending uponthe intact composition of the parent material. Com-

3-6

plete degradation can be facilitated by alternately wet-ting, drying, and disking the material before compac-tion A detailed discussion on the treatment of shalesas a fill material is given in FHWA-RD-78-141.

(5) Marginal materials. Marginal materials arethese materials that because of either their poor com-paction, consolidation, or swelling characteristicswould not normally be used as backfill if sources ofsuitable material were available. Material consideredto be marginal include fine-grained soils of high plas-ticity and expansive clays. The decision to use mar-ginal materials should be based on economical andenergy conservation considerations to include the costof obtaining suitable material whether from a distantborrow area or commercial sources, possible distressrepair costs caused by use of marginal material, andthe extra costs involved in processing, placing, andadequately compacting marginal material.

(a) The fine-grained, highly plastic materialsmake poor backfill because of the difficulty in han-dling, exercising water-content control, and com-pacting. The water content of highly plastic fine-grained soils is critical to proper compaction and isvery difficult to control in the field by aeration or wet-ting. Furthermore, such soils are much more compres-sible than less-plastic and coarse-grained soils; shearstrength and thus earth pressures may fluctuate be-tween wide limits with changes in water content; andin cold climates, frost action will occur in fine-grainedsoils that are not properly drained. The only soil typein this category that might be considered suitable asbackfill is inorganic clay (CH). Use of CH soils shouldbe avoided in confined areas if a high degree of com-paction is needed to minimize backfill settlement or toprovide a high compression modulus.

(b) The swelling (and shrinking) characteristicsof expansive clay vary with the type of clay mineralpresent in the soil, the percentage of that clay mineral,and the change in water content. The active clay min-erals include montmorillonite, mixed-layer combina-tions of montmorillonite and other clay minerals, andunder some conditions chlorites and vermiculites.Problems may occur from the rise of groundwater,seepage, leakage, or elimination of surface evaporationthat may increase or decrease the water content ofcompacted soil and lead to the tendency to expand orshrink. If the swelling pressure developed is greaterthan the restraining pressure, heave will occur andmay cause structural distress. Compaction on the wetside of optimum moisture content will produce lowermagnitudes of swelling and swell pressure. Expansiveclays that exhibit significant volume increases shouldnot be used as backfill where the potential for struc-tural damage might exist. Suitability should be basedupon laboratory swell tests (TM 5-818-1/AFM 88-3,Chapter 7).

(c) Additives, such as hydrated lime, quicklime,and fly ash, can be mixed with some highly plasticclays to improve their engineering characteristics andpermit the use of some materials that would otherwisebe unacceptable. Hydrated lime can also be mixed withsome expansive clays to reduce their swelling char-acteristics (TM 5-818-1/AFM 88-3, Chapter 7). Laboratory tests should be performed to determine theamount of the additive that should be used and thecharacteristics of the backfill material as a result ofusing the additive. Because of the complexity of soil-additive systems and the almost complete empiricalnature of the current state of the art, trial mixes mustbe varified in the field by test fills.

(6) Commercial by-products. The use of commer-cial by-products, such as furnace slag or fly ash asbackfill material, may be advantageous where suchproducts are locally available and where suitable nat-ural materials cannot be found. Fly ash has been usedas a lightweight backfill behind a 25-foot-high walland as an additive to highly plastic clay. The suitabil-ity of these materials will depend upon the desirablecharacteristics of the backfill and the engineeringcharacteristics of the products.3-4. Processing of backfill materials. Theconstruction of subsurface structures often requiresthe construction of elements of the structure within orupon large masses of backfill. The proper functioningof these elements are often critically affected by ad-verse behavioral characteristics of the backfill. Be-havioral characteristics are related to material type,water content during compaction, gradation, and com-paction effort. While compaction effort may be easily

TM 5-818-4/AFM 88-5, Chap. 5

controlled during compaction, it is difficult to controlmaterial type, water content, and gradation of thematerial as it is being placed in the backfill; controlcriteria must be established prior to placement.

a. Material type. Backfill material should consist ofa homogeneous material of consistent and desirablecharacteristics. The field engineer must ensure thatonly the approved backfill material is used and thatthe material is uniform in nature and free of anyanomalous material such as organic matter or claypockets. Stratified material should be mixed prior toplacing to obtain a uniform blend. Excavated materialto be used as backfill should be stockpiled according toclass or type of material.

b. Water content. While water content can be ad-justed to some extent after placing (but before com-pacting), it is generally more advantageous to adjustthe water content to optimum compaction conditionsbefore placing. Adjustment of water content can be ac-complished by aeriation (disking or turning) or sprin-kling the material in 12- to 18- inch layers prior toplacing or stockpiling. If the material is stockpiled,provisions should be made to maintain a constantmoisture content during wet or dry seasons.

c. Ensuring gradation. Some backfill materials con-sisting of crushed rock, gravel, or sand require limita-tions on maximum and minimum particle-size orgradation distributions. Where materials cannot be lo-cated that meet gradation criteria, it may be advanta-geous to require processing of available material bysieving to obtain the desired gradation.

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TM 5-818-4/AFM 88-5, Chap. 5

CHAPTER 4

EARTHWORK: EXCAVATION AND PREPARATION FOR FOUNDATIONS

4-1. Excavation.a. General. In general, excavation for subsurface

structures will consist of open excavation and shaftand tunnel excavation. Where excavation to greatdepths is required, a variety of soils and rock may beencountered at a single site. Soils may range through awide spectrum of textures and water contents. Rockencountered may vary from soft rock, very similar to afirm soil in its excavation requirements, to extremelyhard rock requiring extensive blasting operations forremoval. Groundwater may or may not be present. Thegroundwater conditions and the adequacy of ground-water control measures are important factors in exca-vation, in maintaining a stable foundation, and inbackfilling operations. The extent to which ground-water can be controlled also influences the slopes towhich the open excavation can be cut, the bracing re-quired to support shaft and tunnel excavation, and thehandling of the excavated material.

b. Good construction practices, and problems. Amajority of the problems encountered during excava-tion are related to groundwater conditions, slope sta-bility, and adverse weather conditions. Many of theproblems can be anticipated and avoided by precon-struction planning and by following sound construc-tion practices.

(1) Groundwater. Probably the greatest source ofproblems in excavation operations is groundwater. Ifthe seepage of groundwater into an excavation is ade-quately controlled, other problems will generally beminor and can be easily handled. Several points shouldbe recognized that, if kept in mind, will help to reduceproblems attributable to groundwater. In some in-stances, groundwater conditions can be more severethan indicated by the original field exploration investi-gation since field explorations provide informationonly for selected locations and may not provide a truepicture of the overall conditions.

(a) If groundwater seepage begins to exceed thecapacity of the dewatering system, conditions shouldnot be expected to improve unless the increased flow isknown to be caused by a short-term condition such asheavy rain in the area. If seepage into the excavationbecomes excessive, excavation operations should behalted until the necessary corrective measures are de-termined and effected. The design and evaluation ofdewatering systems require considerable experience

that the contractor or the contracting office often donot possess, and the assistance of specialists in thisfield should be obtained.

(b) Groundwater without significant seepageflow can also be a problem since excess hydrostaticpressures can develop below relatively imperviousstrata and cause uplift and subsequent foundation orslope instability. Excess hydrostatic pressures can alsooccur behind sheet pile retaining walls and shoringand bracing in shaft and tunnel excavations. Visual ob-servations should be made for indications of trouble,such as uncontrolled seepage flow, piping of materialfrom the foundation or slope, development of soft wetareas, uplift of ground surface, or lateral movements.

(c) Accurate daily records should be kept of thequantity of water removed by the dewatering systemand of the piezometric levels in the foundation and be-neath excavation slopes. Separate records should bekept of the flow pumped by any sump-pump system re-quired to augment the regular dewatering system tonote any increase of flow into the excavation. Flow-meters or other measuring devices should be installedon the discharge of these systems for measurementpurposes (TM 5-818-5/NAVFAC P-418/AFM 88-5,Chap. 6). These records can be invaluable in evaluating“Changed Condition” claims submitted by the contrac-tor. The contractor should be required to have “stand-by” equipment in case the original equipment breaksdown.

(2) Surface water. Sources of water problemsother than groundwater are surface runoff into the ex-cavation and snow drifting into the excavation. A pe-ripheral, surface-drainage system, such as a ditch andberm, should be required to collect surface water anddivert it from the excavation, In good weather there isa tendency for the contractor to become lax in main-taining this system and for the inspection personnel tobecome lax in enforcing maintenance. The result canbe a sudden filling of the excavation with water duringa heavy rain and consequent delay in construction. Thesurface drainage system must be constantly main-tained until the backfill is complete. Drifting snow is aseasonal and regional problem, which can best be con-trolled by snow fences placed at strategic locationsaround the excavation,

(3) Slope integrity. Another area of concern dur-ing excavation is the integrity of the excavation

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TM 5-818-4/AFM 88-5, Chap. 5

slopes. The slopes may be either unsupported or sup-ported by shoring and bracing. The lines and grades in-dicated in the plans should be strictly adhered to. Thecontractor may attempt to gain additional workingroom in the bottom of the excavation by steepeningthe slopes; this change in the plans must not be al-lowed.

(a) Where shoring and bracing are necessary toprovide a stable excavation, and the plans and specifi-cations do not provide details of these requirements,the contractor should be required to submit the plansin sufficient detail so that they can be easily followedand their adequacy checked. The first principle of ex-cavation stabilization, using shoring and bracing, isthat the placing of supports should proceed with exca-vation. The excavation cut should not be allowed toyield prior to placing of shoring and bracing since thelateral pressures to be supported would generally beconsiderably greater after yield of the unshored cutface than if no movement had occurred prior to place-ment of the shoring. Excavation support systems arediscussed in TM 5-818-1/AFM 88-3, Chapter 7. Allsafety requirements for shoring and bracing as con-tained in EM 385-1-1 should be strictly enforced.

(b) The inspector must be familiar with stockpil-ing requirements regarding the distance from thecrest of the excavation at which stockpiles can be es-tablished and heavy equipment operated without en-dangering the stability of the excavation slopes. Hemust also know the maximum height of stockpile orweight of equipment that can be allowed at this dis-tance.

(c) Excessive erosion of the excavation slopesmust not be permitted. In areas subject to heavy rain-fall, it may be necessary to protect excavation slopeswith polyethylene sheeting, straw, silt fences, or byother means to prevent erosion. Excavation slopes forlarge projects that will be exposed for several seasonsshould be vegetated and maintained to prevent ero-sion.

(4) Stockpiling excavated material. Generally,procedures for stockpiling are left to the discretion ofthe contractor. Prior to construction, the contractormust submit his plans for stockpiling to the contract-ing officer for approval. In certain cases, such as wherethere are different contractors for the excavation andthe backfill phases, it may be necessary to include thedetails for stockpiling operations in the specifications.In either case, it is important that the stockpiling pro-cedures be conducive to the most advantageous use ofthe excavated materials.

(a) As the materials are excavated, they shouldbe separated into classes of backfill and stockpiled ac-cordingly. Thus the inspection personnel controllingthe excavation should be qualified to classify the mate-rial and should be thoroughly familiar with backfill re-

4-2

quirements. Also, as the materials are placed in stock-piles, water should be added or the materials should beaerated as required to approximate optimum watercontent for compaction. Field laboratory personnel canassist in determining the extent to which this is neces-sary. The requirements of shaping the stockpile todrain and sealing it against the entrance of undesir-able water by rolling with spreading equipment orcovering with polyethylene sheeting should be en-forced. This step is particularly important for cohesivesoils that exhibit poor draining characteristics andtend to remain wet if once saturated by rains. Stock-piles must be located over an area that is large enoughto permit processing and where they will not interferewith peripheral drainage around the excavation andwill not overload the slopes of the excavation.

(b) In cases where significant energy and costsaving can be realized, special stockpiling require-ments should be implemented. An example would be alarge project consisting of a number of excavation andbackfilling operations. The excavation material fromthe first excavation could be stockpiled for use as back-fill in the last excavation. The material from the inter-mediate excavations could in turn be immediately usedas backfill for the first, second, etc., phases of the proj-ect and thereby eliminate double handing of excavatedbackfill for all but the first-phase excavation.

(5) Protection of exposed material. If materialsthat are exposed in areas, such as walls of a silo shaft,foundation support, or any other area against whichconcrete will be placed, are susceptible to deteriorationor swell when exposed to the weather, they should beproperly protected as soon after exposure as possible.Depending on the material and protection require-ments, this protection may be pneumatic concrete, as-phalt spray, or plastic membrane (TM 5-818-1/AFM88-33, Chap. 7). In the case of a foundation area, thecontractor is required to underexcavate leaving a coverfor protection, as required, until immediately prior toplacement of the structure foundation. Any frost-sus-ceptible materials encountered during excavationshould be protected (para 2-3h (3) and (4)) if the exca-vation is to be left open during an extended period offreezing weather.

(6) Excavation record. As the excavation pro-gresses, the project engineer should keep a daily recordof the type of material excavated and the progressmade. This record would be of value if subsequentclaims of “Changed Conditions” are made by the con-tractor.

4-2. Foundation preparation.a. General. In this manual, preparation applies to

foundations for backfill as well as those for structuresto be placed in the excavation. Generally, if proper ex-cavation procedures have been followed, very little ad-

ditional preparation will be required prior to backfillplacement.

b. Good construction practices, and problems. Asmentioned previously, the problems associated withfoundation preparation are greatly reduced by follow-ing such proper excavation procedures as maintaininga dry excavation and planning ahead. The principles ofgood foundation preparation are simple, but enforcingthe provisions of the specifications concerning thework is more difficult. Inspection personnel mustrecognize the importance of this phase of the worksince, if not properly controlled, problems can result.

(1) It is most important that a stable foundationbe provided. Thus it may be necessary, particularly inthe case of sensitive fine-g-rained materials, to requirethat the final excavation for footings be carefully donewith hand tools and that no equipment be allowed tooperate on the final cut surface. To provide a workingplatform on which to begin backfill placement on thesesensitive materials, it may be necessary to place aninitial layer of granular material.

(2) If the foundation is to be supported on rock,the soundness of the exposed rock should be checkedby a slaking test (soaking a piece of the rock in waterto determine the resulting degree of deterioration(para 3-2b (6)) and visual observation to determine ifthe rock is in a solid and unshattered condition. If re-moval of rock below the foundation level is required,the space should be filled with concrete. A qualifiedgeological or soils engineer should inspect the area if itis suspected that the material will deteriorate or swellwhen exposed to the weather. If necessary, the mate-rials must be protected from exposure using themethods previously discussed in paragraph 4-1b (5).

(3) Before placement of any structure foundationis begun, the plans should be rechecked to ensure thatall required utilities and conduits under or adjacent tothe foundation have been placed, so that excavatingunder or undermining the foundation to place utilitiesand conduits will not become necessary later.

(4) Occasionally, it may be found upon completionof the excavation that if a structure were placed asshown on the plans, it would be supported on two ma-terials with drastically different consolidation charac-tertistics, such as rock and soil, rock and backfill, orundisturbed soil and backfill. This situation could oc-

TM 5-818-4/AFM 88-5, Chap. 5

cur because the predesign subsurface information wasinadequate, because the structure was relocated or re-oriented by a subsequent change in the plans, becauseof an oversight of the design engineer, or because ofthe excavation procedures followed by the contractor.Regardless of the reason, measures such as overexca-vation and placement of subsequent backfill should betaken, where possible, and in coordination with the de-sign office to provide a foundation of uniform materi-al. Otherwise, the design office should evaluate thedifferences in foundation conditions for possiblechanges to the structural foundation elements.

(5) Preparing the area to receive the backfill con-sists of cleaning, leveling, and compacting the bottomof the excavation if the foundation is in soil. All debrisand foreign material, such as trash, broken concreteand rock, boulders, and forming lumber, should be re-moved from the excavation. All holes, depressions,and trenches should be filled with the same material asthat specified to be placed immediately above such adepression, unless otherwise designated, and com-pacted to the density specified for the particular ma-terial used. If the depression is large enough to accom-modate heavy compacting equipment, the sides of thedepression should have a positive slope and be flatenough for proper operation of compaction equipment.After the area is brought to a generally level conditionby compacting in lifts in accordance with specifica-tions, the entire area to receive backfill should be sacri-ficed to the depth specified, the water content ad-justed if necessary, and the area compacted as speci-fied. If the foundation is in rock, the area should beleveled as much as possible and all loose material re-moved.

(6) All work in the excavation should be accom-plished in the dry; therefore, the dewatering systemshould be operated for the duration of this work.Under no circumstances should the contractor be al-lowed to dry an area by dumping a thick layer of drymaterial over it to blot the excess water. If soil existsat the foundation level and becomes saturated, it can-not be compacted. The saturated soil will have to be re-moved and replaced or drained sufficiently so that itcan be compacted. Any frozen material in the founda-tion should be removed before placement of concretefootings or compacted backfill.

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TM 5-818-4/AFM 88-5, Chap. 5

CHAPTER 5

BACKFILL OPERATIONS

5-1. Placement of backfill.a. General. Backfill construction is the refilling of

previously excavated space with properly compactedmaterial. The areas may be quite large, in which casethe backfilling operation will be similar to embank-ment construction. On the other hand, the areas maybe quite limited, such as confined areas around or be-tween and beneath concrete or steel structures andareas in trenches excavated for utility lines. Prior toconstruction of the backfill, the inspection personnelshould become thoroughly familiar with the variousclasses of backfill to be used. They should be able toreadily identify the materials on sight, know wherethe various types of material should be placed, and befamiliar with the compaction characteristics of the soiltypes. Compaction characteristics of various soil typesare discussed in appendix B.

b. Good construction practices, and problems. Problems with placement of backfill will vary from one con-struction project to another. The magnitude of theproblems will depend on the type of materials avail-able such as backfill, density requirements, and theconfiguration of the areas in which compaction is to beaccomplished. Problems should be expected during theinitial stages of backfill compaction unless the con-tractor is familiar with compaction characteristics ofbackfill materials. The inspector can be of great as-sistance to the contractor during this period by per-forming frequent water content and density checks.The information from these checks will show the con-tractor the effects of the compaction procedures beingused and point out any changes that should be made.

(1) Backfilling procedures. Problems associatedwith the compaction of backfill can be minimized byfollowing good backfilling procedures. Good back-filling procedures include: processing the material(para. 3-4) before it is placed in the excavation; plac-ing the material in a uniformly spread loose lift of theproper thickness suited to the compaction equipmentand the type of material to be used; applying the neces-sary compaction effort to obtain the required densi-ties; and ensuring that these operations are not per-formed during adverse weather. Proper bond should beprovided between each lift and also between the back-fill and the sides of the excavation.

(2) Compaction equipment, backfill material, andzones. The type of compaction equipment used. to

achieve the required densities will usually dependupon the type of backfill material being compactedand the type of zone in which the material is placed.

(a) In open zones, coarse-grained soils that ex-hibit slight plasticity (clayey sands, silty sands, clayeygravels, and silty gravels) should be compacted witheither sheepsfoot or rubber-tired rollers; close controlof water content is required where silt is present insubstantial amounts. For sands and gravelly sandswith little or no fines, good compaction results are ob-tained with tractor compaction. Good compaction canalso be achieved in gravels and gravel-sand mixtureswith either a crawler tractor or rubber-tired and steel-wheeled rollers. The addition of vibration to any of themeans of compaction mentioned above will usually im-prove the compaction of soils in this category. In con-fined zones, adequate compaction of cohesionless soilsin either the air-dried or saturated condition can beachieved by vibratory-plate compactors with a staticweight of at least 100 pounds. If the material is com-pacted in the saturated condition, good compactioncan be achieved by internal vibration (for example, byusing concrete vibrators). Downward drainage is re-quired to maintain seepage forces in a downward di-rection if the placed material is saturated to aid incompaction.

(b) Inorganic clays, inorganic silts, and veryfine sands of low to medium plasticity are fairly easilycompacted in open zones with sheepsfoot or rubber-tired rollers in the 15,000-pound and above wheel-loadclass. Some inorganic clays can be adequately com-pacted in confined zones using rammer or impact com-pactors with a static weight of at least 100 pounds pro-vided close control of lift thickness and water contentis maintained.

(c) Fine-grained, highly plastic materials,though not good backfill materials, can best be com-pacted in open zones with sheepsfoot rollers. Sheeps-foot rollers leave the surface of the backfill in a roughcondition, which provides an excellent bond betweenlifts. In confined areas the best results, which are notconsidered good, are obtained with rammer or impactcompactors.

(3) Lift thickness. The loose-lift thickness will de-pend on the type of backfill material and the compac-tion equipment to be used.

(a) As a general rule, a loose-lift thickness thatwill result in a 6-inch lift when compacted can be al-

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TM 5-818-4/AFM 88-5, Chap. 5

lowed for most sheepsfoot and pneumatic-tired rollers.Cohesive soils placed inapproximately lo-inch looselifts will compact to approximately 6 inches, and cohe-sionless soils placed in approximately 8-inch base liftswill compact to 6 inches. Adequate compaction can beachieved in cohesionless materials of about 12- to 15-inch loose-lift thickness if heavy vibratory equipmentis used. The addition of vibration to rolling equipmentused for compacting cohesive soils generally has littleeffect on the lift thickness that can be compacted, al-though compaction to the desired density can some-times be obtained by fewer coverages of the equip-ment.

(b) In confined zones where clean cohesionlessbackfill material is used, a loose-lift thickness of 4 to 6inches and a vibratory plate or walk-behind, dual-drumvibratory roller for compaction is recommended.Where cohesive soils are used as backfill in confinedzones, use of rammer compactors and a loose-lift thick-ness of not more than 4 inches should be specified. Ex-perience has shown that “two-by-four” wood rammers,or single air tampers (commonly referred to as“powder puffs” or “pogo sticks”) do not produce suffi-cient compaction.

(4) Density requirements. In open areas of backfillwhere structures will not be constructed, compactioncan be less than that required in more critical zones.Compaction to 90 percent of CE 55 maximum drydensity as obtained by MIL-STD-621 should be ade-quate in these areas. If structures are to be constructedon or within the backfill, compaction of cohesionlesssoils to within 95 to 100 percent of CE 55 maximumdry density and of cohesive soils to at least 95 percentof CE 55 should be required for the full depth of back-fill beneath these structures. The specified degree ofcompaction should be commensurate with thetolerable amount of settlement, and the compactionequipment used should be commensurate with the al-lowable lateral pressure on the structure. Drainageblankets and filters having special gradation require-ments should be compacted to within 95 to 100 per-cent of CE 55 maximum dry density. Table 5-1 gives asummary of type of compaction equipment, number ofcoverages, and lift thickness for the specified degree ofcompaction of various soil types (TM 5-818-1/AFM88-3, Chap. 7).

(5) Cold weather. In areas where freezingtemperatures either hamper or halt construction dur-ing the winter, certain precautions can and should betaken to prevent damage from frost penetration andsubsequent thaw. Some of these precautions are pre-sented below.

(a) Placement of permanent backfill should bedeferred until favorable weather conditions prevail.However, if placement is an absolute necessity duringfreezing temperatures, either dry, cohesionless, non-

5-2

frost-susceptible materials or material containing ad-ditives, such as calcium chloride, to lower the freezingtemperature of the soil water should be used. Each liftshould be checked for frozen material after compac-tion and before construction of the next lift is begun.If frozen material is found, it should be removed; itshould not be disked in place. Additives should not beused indiscriminately since they will ordinarily changecompaction and water content requirements. Priorlaboratory investigation should be conducted to deter-mine additive requirements and the effect on the com-paction characteristics of the backfill material.

(b) Under no circumstances should frozen ma-terial, from stockpile or borrow pit, be placed in back-fill that is to be compacted to a specified density.

(c) Prior to halting construction during thewinter, the peripheral surface drainage system shouldbe checked and reworked where necessary to providepositive drainage of surface water away from the exca-vation.

(d) Foundations beneath structures and backfillaround structures should not be allowed to freeze, be-cause structural damage will invariably develop.Structures should be enclosed as much as possible andheated if necessary. Construction should be scheduledso as to minimize the amount of reinforcing steel pro-truding from a partially completed structure sincesteel will conduct freezing temperatures into thefoundation.

(e) Permanent backfill should be protected fromfreezing as discussed in paragraphs 2-3h (3) and (4).Records should be made of all temporary coveringsthat must be removed before backfilling operations areresumed. A checklist should be maintained to ensurethat all temporary coverings are removed at the begin-ning of the next construction season.

(f) During freezing weather, records should bekept of the elevation of all critical structures to whichthere is the remotest possibility of damage or move-ment due to frost heave and subsequent thaw. It is im-portant that frost-free bench marks be established towhich movement of any structure can be referenced.Bench marks also should be established on the struc-tures at strategic locations prior to freezing weather.

(g) At the beginning of the following construc-tion season and after the temporary insulating cover-ings are removed, the backfill should be checked forfrozen material and ice lenses, and the density of thecompacted material should be checked carefully beforebackfilling operations are resumed. If any backfill haslost its specified density because of freezing, it shouldbe removed.

(6) Zones having particular gradation require-ments. Zones that have particular gradation require-ments include those needed to conduct and controlseepage, such as drainage blankets, filters, and zones

TM 5-818-4/AFM 88-5, Chap. 5

Table 5-1. Summary of Compaction Criteria a

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TM 5-818-4/AFM 88-5, Chap. 5

susceptible to frost penetration. Drainage zones are of-ten extremely important to the satisfactory construc-tion and subsequent performance of the structure. Tomaintain the proper functioning of these zones, caremust be taken to ensure that the material placed hasthe correct gradation and is compacted according tospecifications.

c. Special problems. In open zones, compaction ofbackfill will not generally present any particular prob-lems if proper compaction procedures normally associ-ated with the compaction of soils are exercised and thematerials available for use, such as backfill, are not un-usually difficult to compact. The majority of the prob-lems associated with backfill will occur in confinedzones where only small compaction equipment produc-ing a low compaction effort can be used or where be-cause of the confined nature of the backfill zone evensmall compaction equipment cannot be operated effec-tively.

(1) Considerable latitude exists in the varioustypes of small compaction equipment available. Unfor-tunately, very little reliable information is available onthe capabilities of the various pieces of equipment. De-pending upon the soil type and working room, it maybe necessary to establish lift thickness and compactioneffort based essentially on trial and error in the field.For this reason, close control must be maintainedparticularly during the initial stages of the backfill un-til adequate compaction procedures are established.

(2) Circular, elliptical and arched walled struc-tures are particularly difficult to adequately compactbackfill beneath the under side of haunches because oflimited working space. Generally, the smaller thestructure the more difficult it is to achieve requireddensities. Rock, where encountered, must be removedto a depth of at least 6 inches below the bottom of thestructure and the overdepth backfilled with suitablematerial before foundation bedding for the structure isplaced. Some alternate bedding and backfill placementmethods are discussed below.

(a) One method is to bring the backfill to theplanned elevation of the spring line using conventionalheavy compaction equipment and methods. A tem-plate in the shape of the structure to be bedded is thenused to reexcavate to conform to the bottom contoursof the structure. If the structure is made of corrugatedmetal, allowance should be made in the grade for pene-tration of the corrugation crests into the backfill uponapplication of load. Success of this method of beddingis highly dependent on rigid control of grade during re-excavation using the template. This procedure isprobably the most applicable where it is necessary touse a cohesive backfill.

(b) Another method of bedding placement is tosluice a clean granular backfill material into the bedafter the structure is in place. This method is particu-

5-4

of all instruments and necessary apparatus or struc-tures (such as trenches and terminal houses) so thatnecessary arrangements and a schedule for installa-

larly adapted to areas containing a maze of pipes orconduits. Adequate downward drainage, generally es-sential to the success of this method, can be providedby sump pumps or, if necessary, by pumping from wellpoints. Sluicing should be accompanied by vibrating toensure adequate soil density. Concrete vibrators havebeen used successfully for this purpose. This methodshould be restricted to areas where conduits or pipeshave been placed by trenching or in an excavation thatprovides confining sides. Also, this method should notbe used below the groundwater table in seismic zones,since achieving densities high enough to assure stabili-ty in a seismic zone is difficult.

(c) Another method is to place clean, granularbedding material with pneumatic concrete equipmentunder the haunches of pipes, tunnels, and tanks. Thematerial is placed wet and should have an in-place wa-ter content of approximately 15 to 18 percent. A noz-zle pressure of 40 pounds per square inch is required toobtain proper density. Considerable rebound of materi-al (as much as 25 percent by volume when placed withthe hose nozzle pointed vertically downward and 50percent with the nozzle pointed horizontally) occurs atthis pressure. Rebound is the material that bounces offthe surface and falls back in a loose state. However,the method is very satisfactory if all rebound materialis removed. The material can be effectively removedfrom the backfill by dragging the surface in the areawhere material is being placed with a flat-end shovel.Two or three men will be needed for each gunite hoseoperated.

(d) For structures and pipes that can toleratelittle or no settlement, lean grouts containing granularmaterial and various cementing agents, such as port-land cement or fly ash, can be used. This grout may beplaced by either method discussed in (b) and (c) above.However, grouts may develop hard spots (particularlywhere the sluice method is used that could cause segre-gation of the granular material and the cementingagent), which could generate stress concentrations inrigid structures such as concrete pipes. Stress concen-trations may be severe enough to cause structuraldistress. If lean grouts are used as backfill around arigid structure, the structure must be designed towithstand any additional stress generated by possiblehard spots.

5-2. Installation of instruments. Installa-tion of instrumentation devices should be supervised,if not actually done, by experienced personnel fromwithin the Corps of Engineers or by firms that special-ize in instrumentation installation. The resident engi-neer staff must be familiar with the planned locations

tion can be made withfice or firm that will

the contractor and with the of-install the devices. Inspectors

should inspect any instrumentation furnished and in-stalled by the contractor. Records must be made of theexact locations and procedures used for installationand initial observations. Inspectors should ensure thatnecessary extensions are added for the apparatus (suchas lead lines and piezometer tubes) installed within thebackfill as the backfill is constructed to higher eleva-tions. Care must be used in placing and compactingbackfill around instruments that are installed withinor through backfill. Where necessary to preventdamage to instruments, backfill must be placedmanually and compacted with small compaction equip-ment such as rammers or vibratory plates.

TM 5-818-4/AFM 88-5, Chap. 5

5-3. Postconstruction distress. Good backfillconstruction practices and control will minimize thepotential for postconstruction distress. Nevertheless,the possibility of distress occurring is real, and meas-ures must be taken to correct any problems before theybecome so critical as to cause functional problems withthe facility. Therefore, early detection of distress is es-sential. Some early signs of possible distress in-clude: settlement or swelling of the backfill aroundthe structure; sudden or gradual change of instrumen-tation data; development of cracks in structural walls;and adverse seepage problems. Detailed constructionrecords are important for defining potential distressareas and assessing the mechanisms causing thedistress.

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TM 5-818-4/AFM W-5, Chap. 5

CHAPTER 6

SPECIFICATION PROVISIONS

6-1. General.a. The plans and specifications define the project in

detail and show how it is to be constructed. They arethe basis of the contractor’s estimate and of the con-struction contract itself. The drawings show the physi-cal characteristics of the structure, and the specifica-tions cover the quality of materials, workmanship, andtechnical requirements. Together they form the guideand standard of performance that will be required inthe construction of the project. Once the contract islet, the plans and specifications are binding on boththe Contracting Officer and the contractor and arechanged only by written agreement. For this reason, itis essential that the contractor and the Contracting Of-ficer’s representative anticipate and resolve dif-ferences that may arise in interpreting the intent andrequirements of the specifications. The ease withwhich this can be accomplished will depend on theclarity of the specifications and the background andexperience of the individuals concerned. Understand-ing of requirements and working coordination can beimproved if unusual requirements are brought to theattention of prospective bidders and meetings for dis-cussion are held prior to construction. Situations willundoubtedly arise that are not covered by the speci-fications, or conditions may occur that are differentfrom those anticipated. Close cooperation is requiredbetween the contractor and the inspection personnel inresolving situations of this nature; if necessary, to befair to both parties a change order should be issued.

b. Preparation of contract specifications is easier ifan outline of general requirements is available to thespecification writer. However, it would be virtually im-possible to prepare a guide specification that antici-pates all problems that may occur on all projects.Therefore, contract specifications must be written tosatisfy the specific requirement of each project. Somealternate specification requirements that might beconsidered for some projects are discussed below.

6-2. Excavation. The section of the specificationsdealing with excavation contains information ondrainage, shoring and bracing, removal and stock-piling, and other items, and refers to the plans forgrade requirements and slope lines to be followed inexcavating overburden soils and rock.

a. Drainage. For some projects the specifications

will require the contractor to submit a plan of his exca-vation operations to the Contracting Officer for re-view. The plans and specifications will require that theexcavation and subsequent construction and backfillbe carried out in the dry. To meet this requirement, adewatering system based on the results of ground-water studies may be included in the plans. Also, forsome projects the specifications may require the con-tractor to submit his plan for controlling groundwaterconditions. The specifications should likewise indicatethe possibility of groundwater conditions being dif-ferent from those shown in the subsurface investiga-tion report due to seasonal or unusual variations or in-sufficient information, since the contractor will beheld responsible for controlling the groundwater flowinto the excavation regardless of the amount. To thisend, the specifications should provide for requiring thecontractor to submit a revised dewatering plan for re-view where the original dewatering plan is found to beinadequate.

b. Shoring and bracing. The specifications eitherwill require the contractor to submit for review hisplans for the shoring and bracing required for excava-tion or will specify shoring and bracing required bysubsurface and groundwater conditions and details ofthe lines and grades of the excavation. In the lattercase, the contractor may be given the option to submitalternate plans for shoring and bracing for review bythe Contracting Officer. The plans will present thenecessary information for the design of such a systemif the contractor is allowed this option.

c. Stockpiling. Provisions for stockpiling materialsfrom required excavation according to type of backfillmay or may not be included in the specifications. Gen-erally, procedures for stockpiling are left to the discre-tion of the contractor, and a thorough study should bemade to substantiate the need for stockpiling beforesuch procedures are specified. There are several condi-tions under which inclusion of stockpiling proceduresin the specifications would be desirable and justified.Two such conditions are discussed in the followingparagraphs.

(1) Under certain conditions, such as those thatexisted in the early stages of missile base constructionwhere time was an important factor, it may be neces-sary or desirable to award contracts for the work inphases. As a result, one contractor may do the excavat-

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TM 5-818-4/AFM 88-5, Chap. 5

ing and another place the backfill. It is probable thatthe excavation contractor will have little or no interestin stockpiling the excavated materials in a mannerconducive to good backfilling procedures. When such asituation can be foreseen, the specifications should setforth stockpiling procedures. The justification for suchrequirements would be economy and optimum use ofmaterials available from required excavation as back-fill.

(2) The specifications will contain provisions forremoving, segregating, and stockpiling or disposing ofmaterial from the excavation and will refer to theplans for locations of the stockpiles. The subsoil condi-tions and engineering characteristics requirementsmay state that the specifications must be quite defi-nite concerning segregation and stockpiling proce-dures so that the excavated materials can be used mostadvantageously in the backfill. The specification mayrequire that water be added to the material or the ma-terial be aerated as it is stockpiled to approximate opti-mum water content, that the stockpile be shaped todrain and be sealed from accumulation of excess wa-ter, and that the end dumping of material on the stock-pile be prohibited to prevent segregation of materialsize or type along the length of the stockpile.

(3) An alternative to this latter action would be tospecify the various classes of backfill required andleave the procedure for stockpiling the materials bytype to the discretion of the contractor. In this case,the contractor should be required to submit a detailedplan for excavating and stockpiling the material. Theplan should indicate the location of stockpiles for vari-ous classes of backfill so that the material can betested for compliance with the specifications. The con-tractor may elect to obtain backfill material from bor-row or commercial sources rather than to separate andprocess excavated materials. Then the specificationsshould require that stockpiles of the various classes ofneeded backfill be established at the construction sitein sufficient quantity and far enough in advance oftheir use to allow for the necessary testing for approv-al unless conditions are such that approval of the sup-plier’s stockpile or borrow source can be given.

6-3. Foundation preparation. The provisionsfor preparation for structures will generally not begrouped together in the specifications but will appearthroughout the earthwork section of the specificationsunder paragraphs on excavation, protection of founda-tion materials, backfill construction, and concreteplacement. When a structure is to be founded on rock,the specifications will require that the rock be firm,unshattered by blasting operations, and not de-teriorated from exposure to the weather. The contrac-tor will be required to remove shattered or weatheredrock and to fill the space with concrete.

6-2

a. Specifications for structures founded on soil re-quire the removal of all loose material and all unsuit-able material, such as organic clay or silt, below thefoundation grade. When doubt exists as to the suitabil-ity of the foundation materials, a soils engineer shouldinspect the area and his recommendations should befollowed. When removal of rock material below theplanned foundation level is required, the overexcava-tion will usually require filling with concrete. Thespecifications also require dewatering to the extentthat no backfill or structural foundation is placed inthe wet.

b. Specifications for preparation of the soil founda-tion to receive backfill require removing all debris andforeign matter, making the area generally level, andscarifying, moistening, and compacting the founda-tion to a specified depth, generally 12 inches. Specificprovisions may or may not be given with respect to lev-eling procedures.

6-4. Backfill operations. The specifications de-fine the type or types of material to be used for backfillconstruction and provide specific instructions as towhere these materials will be used in the backfill, Thepercentage of CE 55 maximum dry density to be ob-tained, determined by a designated standard labora-tory compaction procedure, will be specified for thevarious zones of backfill. The maximum loose-liftthickness for placement will also be specified. Becauseof the shape of the compaction curve (see discussion ofcompaction characteristics in Section B-1, app. B), thedegree of compaction specified can be achieved onlywithin a certain range of water contents for a particu-lar compaction effort. Though not generally specifiedin military construction, the range of water contents isan important factor affecting compaction.

a. The specifications sometimes stipulate the char-acteristics and general type of compaction equipmentto be used for each of the various types of backfill.Sheepsfoot or rubber-tired rollers, rammer or impactcompactors, or other suitable equipment are specifiedfor fine-grained, plastic materials. Noncohesive, free-draining materials are specified to be compacted bysaturating the material and operating crawler-typetractor, surface or internal vibrators, vibratory com-pactors, or other similar suitable equipment. Thespecifications generally will prohibit the use of rock orrock-soil mixtures as backfill in this type of construc-tion. However, when the use of backfill containingrock is permitted, the maximum size of the rock is giv-en in the specifications along with maximum lift thick-ness, loading, hauling, dumping, and spreading proce-dures, type of compaction equipment, and method ofequipment operation. The specifications should pro-hibit the use of rock or rock-soil mixtures as backfill in

TM 5-818-4/AFM 88-5, Chap. 5

areas where heavy equipment cannot operate. Rock-soil mixtures having greater than 8 to 10 percent bind-er should be prohibited in all areas. In the case of back-fill containing rock, the density is not generally speci-fied. Obtaining adequate density is usually achievedby specifying the compaction procedures. The specifi-cations may require that these procedures be devel-oped in field test sections.

b. Specifications may also require specific equip-ment and procedures to ensure adequate bedding forround-bottom structures such as tunnels, culverts, con-duits, and tanks. Procedures normally specified forplacement of bedding for these types of structures arediscussed in paragraph 5-1c (2).

c. The specifications will state when backfill may beplaced against permanent concrete construction withrespect to the time after completion; this time periodis usually from 7 to 14 days. To provide adequate pro-tection of the structures during backfill construction,the specifications require that the backfill be built upsymmetrically on all sides and that the area of opera-tion of heavy equipment adjacent to a structure be lim-ited. Also, the minimum thickness of compacted mate-rials to be placed over the structures by small compac-

tion equipment, such as vibratory plate or rammertype, will be specified before heavy equipment is al-lowed to operate over the structure. The specificationsrequire that the surface of the backfill be sloped todrain at all times when necessary to prevent pondingof water on the fill. The specifications also provide forgroundwater control, so that all compacted backfillwill be constructed in the dry. Where select, free-draining, cohesionless soils of high permeability are re-quired in areas where compaction is critical, thespecifications list gradation requirements. Gradationrequirements are also specified for materials used fordrains and filters.

d. Unusually severe specification requirements maybe necessary for backfill operations in confined areas.The requirements may include strict backfill material-type limitation, placement procedures, and compac-tion equipment.

e. It is not the policy of the Government to informthe contractor of ways to accomplish the necessaryprotection from freezing temperatures. However, toensure that adequate protection is provided, it may benecessary to specify that the contractor submit de-tailed plans for approval for such protection.

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TM 5-818-4/AFM 88-5, Chap. 5

CHAPTER 7

CONSTRUCTION CONTROL

7-l. General. The heterogeneous nature of soilmakes it the most variable construction material withwhich engineers are required to work. Research in soilmechanics and experience gained recently in con-structing large earth embankments have provided ad-ditional knowledge toward understanding and predict-ing the behavior of a soil as a construction material.However, only with careful control can engineers en-sure that backfill construction will satisfactorily fulfillthe intended functions. Both the contractor and theGovernment share dual responsibility in achieving asatisfactory product. The contractor is responsible forinspection and tests through his quality control sys-tem. The Government’s responsibility is assuring thatthe contractor’s quality control system is achieving thedesired results through its quality acceptance system.

a. Contractor quality control. The contractor is re-sponsible for all of the activities that are necessary toensure that the finished work complies with the plansand specifications to include quality control require-ments, supervision, inspection, and testing. The con-struction contract special provisions explain the qual-ity control system that the contractor must establish;the technical provisions specify the construction re-quirements with the tests, inspections, and submittalsthat the contractor must follow to produce acceptablework.

(1) Prior to construction, the contractor must sub-mit for approval by the Contracting Officer his planfor controlling construction quality. The plan mustcontain all of the elements outlined in the special pro-visions and demonstrate a capability for controlling allof the construction operations specified in the tech-nical provisions. The plan must include the personnel(whether contractor’s personnel or outside privatefirm) and procedures the contractor intends to use forcontrolling quality, instructions and authority he isgiving his personnel, and the report form he will use.The plan should be coordinated with his project con-struction schedule.

(2) During construction, the contractor is respon-sible for exercising day by day construction qualitycontrol in consonance with his accepted control plan.He must maintain current records of his quality con-trol operations. Reports of his operations must be sub-mitted at specified intervals and be in sufficient detailto identify each specific test.

(3) The prime contractor is responsible for the

quality control of all work including any work by subcontractors.

b. Corps acceptance control. In contrast to the con-tractor’s quality control, the Government is responsi-ble for quality assurance, which includes: the checks,inspections, and tests of the products that comprisethe construction; the processes used in the work; andthe finished work for the purpose of determiningwhether the contractor’s quality control is effectiveand he is meeting the requirements of the contract.These activities are to assure that defective work ormaterials are not incorporated in the construction.

c. Coordination between Government and contrac-tor. The contractor’s quality control does not relievethe Contracting Officer from his responsibility forsafeguarding the Government’s interest. The qualityassurance inspections and tests made by the Govern-ment may be carried out at the same time and adjacentto the contractor’s quality control operations. Qualitycontrol and quality assurance supplement one anotherand assist in avoidance of construction deficiencies orin early detection of such deficiencies when they canbe easily corrected without requiring later costly tearout and rebuild. The remainder of this chapter discuss-es the Corps quality assurance activities.

7-2. Corps acceptance control organiza-tion.

a. General. Difficulties in construction of a com-pacted backfill can be attributed at least in part to in-experience of the control personnel in this phase ofconstruction work or lack of emphasis as to the impor-tance of proper procedure and control. Since it is es-sential that policies with regard to control be estab-lished prior to the initiation of construction, thoroughknowledge of the capabilities of the control organiza-tion and of the intent of the plans and specifications isrequired. Control is achieved by a review of construc-tion plans and specifications, visual inspection of con-struction operations and procedures, and physical test-ing. A well-organized, experienced inspection force canmean the difference between a good job and a poorone. A good field inspection organization must bestaffed and organized so that inspection personnel andlaboratory technicians are on the job when and wherethey are needed. Thus the organization must haveknowledge of the construction at all times.

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TM 5-818-4/AFM 88-5, Chap. 5

b. Inspection personnel training program. Prior toconstruction, the training, guidance, and support re-quired to ensure that the inspection force is fully com-petent should be determined. If experience is lacking,training and supervision become more important andnecessary.

(1) The training program for earthwork inspec-tion personnel should consist of both classroom andfield instruction. During the classroom sessions, thespecifications should be studied, discussed, and inter-preted as to the intent of the designer. The criticalareas of compaction should be pointed out as well asthe location of zoned and transitional areas. The in-spection personnel should be instructed on the variouszones of backfill, types of backfill, density require-ments, and classification and compaction characteris-tics for each class of backfill. Inspection personnelshould also be instructed as to approved sources of bor-row for each type of backfill and borrow pit opera-tions, such as loading procedures to provide uniformmaterials and prewetting to provide uniform moisture.The various types of backfill should be studied, so in-spection personnel can recognize and readily identifythese materials. Jar samples may be furnished forlater reference and comparison; preferably theseshould be samples of the particular soils on which laboratory compaction tests were performed in designstudies. Instructions should be given as to water con-tent control, lift thickness, and most suitable compac-tion equipment for each type of backfill. Inspectionpersonnel should be capable of recommending alter-nate procedures to achieve the desired results whenthe contractor’s procedure is unsuccessful.

(2) Inspection personnel should be made aware ofthe importance of their work by explaining the engi-neering features of the design on which the construc-tion requirements are based. Every opportunity shouldbe taken to assemble the inspection force for discus-sion of construction problems and procedures so thatall can gain knowledge from the experience of others.Inspection personnel should be kept informed of all de-cisions and agreements pertinent to their work thatare made at higher levels of administration. Theyshould be advised of the limits of their authority andcontact with contractor personnel.

(3) Field training of inspection personnel shouldinclude observation of their control techniques and ad-ditional instruction on elements of fieldwork requiringcorrection. Inspection personnel should be instructedin the telltale signs that give visual indications wheth-er sufficient compaction is being applied and properwater content is being maintained (see para 7-5b (4)and EM 1110-2-1911 for discussion of telltale signs).They should develop the ability to determine from vis-ual observations (based on correlations with tests onthe project) that satisfactory compaction is being ob-

7-2

tained so that considerable emphasis can be placed onsuch methods as a control procedure rather than rely-ing on field tests alone. Inspection personnel should becapable of selecting locations at which field densityand moisture determinations should be made. To meetthis requirement they must be present almost continu-ously during compaction operations to observe andnote areas where tests appear to be needed. Laboratorytechnicians should be made available to perform testsso that the inspection personnel will be free to observethe placement and compaction process on another por-tion of the backfill. Inspection personnel should beable to use expedient quick-check field apparatus suchas the Proctor and hand-cone penetrometers (sec. B-3,app. B) to make a rapid check of the field water con-tent to supplement acceptance testing and to serve as aguide in determining areas that should be tested. In-spection personnel should also be well versed in nor-mal testing procedures so they can properly supervisetesting or explain the procedure in case they are ques-tioned by contractor personnel.

(4) It is necessary and important that inspectionpersonnel ascertain their authority and responsibilityat an early stage in the construction. Their policyshould be one of firmness coupled with practicality.The quality of the work should not be compromised;however, unreasonable requirements and restrictionsshould not be placed on the contractor in enforcing thespecifications. If the inspection personnel know theirjob and are fair and cooperative in dealing with thecontractor, they will gain his or her respect and coop-eration and be able to efficiently carry out their re-sponsibilities.

b. Field laboratory facilities. The field laboratory isused for routine testing of construction materials (suchas gradation, water content, compaction, and Atter-berg limits tests) and for determining the adequacy offield compaction. The data obtained from tests per-formed by inspection personnel serve as a basis for de-termining and ensuring compliance with the specifica-tions, for obtaining the maximum benefit from thematerials being used, and for providing a complete rec-ord of the materials placed in every part of the project.The size and type of laboratory required are dependenton the magnitude of the job and the type of structuresbeing built. Where excavation and backfill construc-tion are extensive and widespread, the establishmentof a centrally located field laboratory is generallybeneficial. This laboratory in addition to having equip-ment for on-the-job control will provide a nucleus ofexperienced soils engineers or engineering techniciansfor general supervision and training of inspection per-sonnel. Field control laboratories on the sites may beestablished as necessary during the excavation andbackfill phases of the construction. They may be set up

in an enclosed space allocated by the project officer orin mobile testing laboratories, such as pickup truckswith a camper and equipped with the necessary testingequipment for performance of field density tests, wa-ter content tests, and gradation tests. Another possi-bility is the use of large portable boxes in which equip-ment is stored. When special problems arise and therequired testing equipment is not available at the sitelaboratory, the testing should be performed at the cen-tral laboratory.

7-3. Excavation control techniques. Con-trol to obtain a satisfactory excavation is exercised byenforcement of approved plans, visual observations, athorough knowledge of the contractor’s plan of opera-tion and construction schedule, the dimensions and en-gineering features of the structure(s) to be placed inthe excavation, and vertical and horizontal controlmeasurements to ensure that the proper line and graderequirements are met.

7-4. Foundation preparation controltechniques. The main control technique for ensur-ing proper foundation preparation is visual inspection.Prior to backfill placement, all uncompacted fillshould be removed from those portions of the excava-tion to be backfilled. The items included are road fills,loose material that has fallen into overexcavated areasadjacent to foundations, and construction ramps otherthan those required for access to the excavation. Iden-tification of such items will be easier if the inspectionpersonnel have charted the items on the plans as theywere created, since they are not always easily discerni-ble by visual inspection. It is desirable to control earthbackfill placed in foundation leveling operations bywater content and density tests. Care should be exer-cised to ensure that all subdrains required in the foun-dation are protected by filters and transitional zonesthat are adequate to prevent infiltration of fines fromthe surrounding backfill that might otherwise clog thedrains and undermine structures.

7-5. Backfill quality acceptance control.The necessary authority to assure that compactedbackfill is in compliance with the specifications is giv-en in the specifications. The control consists of in-specting and testing materials to be used, checking theamount and uniformity of soil water content, main-taining the proper thickness of the lifts being placed,and determining the dry unit weight being obtained bythe compaction process. While control consists of all ofthese things, good inspection involves much more.

a. Inspection activities. One of the best inducementsto proper placement and compaction of backfill is thepresence of the inspection personnel when backfill isbeing placed. However, to be of value the inspectormust know his job. He should be familiar with all as-

TM 5-818-4/AFM 88-5, Chap. 5

pects of backfill operation, such as selection and avail-ability of materials, processing, hauling, compaction,and inspection procedures. Some of the most commondeficiencies in inspection personnel activities are asfollows:

(1) Failing to enforce specification requirementsfor preparation of the area for backfill. Often tempo-rary fills, the working platform, debris, and other un-desirable materials are left in the excavation causingweak areas and resulting in greater consolidation inthe backfill.

(2) Failing to be cognizant of detailed site-adaptedplans for stockpiling and placing backfill at specific lo-cations. Without knowledge of these plans, inspectionpersonnel are sometimes forced to make engineeringdecisions beyond their capability, such as on-the-siteapproval of a new material or mixture of materials,and stockpile locations.

(3) Allowing processing of backfill material andadjustment of water content on the fill that shouldhave been accomplished prior to placement. The re-sults are the segregation of grain sizes and the nonuni-form distribution of water content. All major process-ing, including crushing, raking, mixing, and adjustingof water content, must be done in the stockpile or bor-row areas.

(4) Allowing lift thickness that is inconsistentwith equipment capabilities and thicker than that al-lowed by specifications. Field density determinationswill not necessarily detect this inconsistency.

(5) Allowing construction of backfill slopes thatare too steep to obtain the full effect of compactionequipment.

(6) Failing to require that the fill be built up uni-formly in a well-defined pattern. Since the contractor’snext move cannot be predicted, the inspection person-nel cannot adequately plan their operations, and it isdifficult to determine which areas of backfill havebeen tested and approved when the backfill is built upin an unorganized manner.

(7) Allowing segregation of coarse-grained, nonco-hesive materials. This condition is caused by improperhauling, dumping, and spreading techniques.

(8) Allowing the use of compaction equipment notsuited to material being compacted.

(9) Failing to perform sufficient field density test-ing in critical areas.

(10) Allowing material that is too wet or too dryto be compacted.

(11) Failing to require that intermediate backfillsurfaces be shaped to drain during backfilling at otherlocations.

b. Inspection requirements. To properly control andinspect backfill operations, the inspection personnelmust keep informed of the construction schedule at alltimes and be at the site where backfill is being placed.

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TM 5-818-4/AFM 88-5, Chap. 5

The inspection personnel must be thoroughly familiarwith every aspect of the earthwork section of thespecifications and know boundary locations for thevarious zones of material. They should be able to read-ily identify the various classes of backfill and knowtheir compaction characteristics and requirements.Good inspection personnel will also know the compac-tion capabilities of various types of equipment and thematerials that each type is best suited to compact.

(1) To maintain adequate control of compactionoperations, a staff of earthwork inspectors and labora-tory personnel commensurate with the importance ofthe work and size of the operation is essential. Thereshould be at least one inspector at the fill when back-fill is being placed. His sole duty should be inspectionof earthwork. Although he should be familiar with thetesting procedures and capable of directing testing op-erations and selecting locations for testing, he shouldnot be required to perform the tests. Laboratory tech-nicians should be available for this purpose. A discus-sion of the methods and procedures for field densitytesting of the compacted fill is contained in sectionB-3, appendix B.

(2) The specifications should require that neces-sary processing of backfill materials be performed inthe stockpile or borrow pit. Processing includes rakingor crushing to remove oversize material, mixing to pro-vide uniformity, and watering or aerating to attain awater content approximating optimum for compac-tion. An earthwork inspector is required at the stock-pile or borrow pit to enforce these provisions. In addi-tion, this inspector has the duties of classifying thematerials, determining their suitability, and directingthe zone of backfill in which they are to be placed. Heis charged with the responsibility of seeing that thecontractor uses the materials available for backfill inthe most advantageous manner. Generally, the stock-pile or borrow pit inspector relies upon visual inspec-tion and experience to exercise control over these oper-ations. Occasionally, he may require that appropriatetests be performed to confirm his judgment.

(3) The duties of the backfill inspector consist ofchecking the material for suitability as it is placed onthe fill and spread, ensuring that any oversize mate-rial, roots, or trash found in the material is removed,checking the thickness of the lift prior to compaction,checking for uniformity and amount of water content,observing compaction operations, and directing ormonitoring testing of the compacted material for com-pliance with density and water content requirements.

(4) There are many techniques and rule-of-thumbprocedures that the earthwork inspector can and mustresort to for assistance in his work. A few of them arediscussed below; others can be ascertained by inspec-tors meeting together to discuss problems and correc-tive action.

7-4

(a) The thickness of loose lifts can be checkedeasily by probing with a calibrated rod just prior tocompaction. Compaction of lifts too thick for theequipment will not normally be detected by perform-ing density tests on the lift, since adequate compactionmay be indicated by a test made in the upper portionof the lift and the lower portion may still have too lowa density. It is therefore a requisite that lift thicknessbe controlled on a loos&thickness basis prior to com-paction

(b) Checks for proper bond between layers canbe made by digging through a lift after compactionand using a shovel to check this bond. If the soil can beseparated easily along the plane between lifts, suffi-cient bond is not being provided. Backfill materialsshould not be placed on dried or smooth surfaces, asbond will be difficult to obtain.

(c) Inspection personnel should be thoroughlyaware of areas where compaction is critical. Theseareas are the confined spaces around and adjacent tostructures that are not accessible to the rolling andspreading equipment. Although the volume of backfillis usually rather small in these areas, a much higherfrequency of check testing for density is required aswell as a careful check of the quality and water contentof the materials to be placed.

c. Compaction control tests. Compaction tests willhave been performed on representative specimens ob-tained from exploratory sampling prior to construc-tion. The selection of suitable backfill material are infact generally made based on these and other tests. Atleast during the early phases of the backfill operation,density requirements are based on these and in somecases additional preconstruction compaction tests.Conditions may develop that require compaction testsduring backfill operations to establish new density re-quirements. Generally, these changes are the results ofbackfill material deviations. The need for additionalcontrol tests may be ascertained from visual observa-tion and changes in compaction characteristics duringfield compaction. For most backfill materials, qualityacceptance compaction control tests must be per-formed according to the CE 55 test procedure specifiedin MIL-STD-621, the equivalent procedure in ASTMD 1557, or the two-point test procedure (app B). Forsome cohesionless soils where higher maximum drydensities can be obtained using the vibratory (relativedensity) compaction procedure, the specifications mayrequire the vibratory test procedures as specified inEM 1110-2-1906 or ASTM D 2049. Field compactioncontrol and rapid compaction check tests that are usedto supplement the Corps acceptance control tests arediscussed in appendix B.

d. Field moisture-density control techniques. Mois-ture-density control is the most important phase of

backfill operations. The success of ensuring requiredbackfill density often determines the functional serv-ice of the imbedded structure. Good control involvesmany techniques. An experienced inspector will notrely on any one technique but from experience willbase his control on a combination of techniques. Mois-ture-density control techniques may be grouped intothree categories: rule-of-thumb techniques, and indi-rect and direct moisture density measurements.

(1) Rule-of-thumb methods. Rule-of-thumb tech-niques are derived from experience and are based onvisual observations and feel of the material. A rule-of-thumb for judging if the water content of a fine-grained, plastic material is near the optimum watercontent consists of rolling the material between thehands until it forms a thread approximately 1/8 inch indiameter. If the material at this stage tends to crack orcrumble, it is in the proper water content range forcompaction. It will be recognized that this method issimilar to the method of determining the plastic limitof a soil. The methods are similar because the optimumwater content for compaction of a cohesive soilroughly approximates the plastic limit of the soil.

(a) Another good indication of whether theproper water content has been obtained can be deter-mined by observing the compacting equipment. Whena sheepsfoot roller is being used and the soil sticks tothe roller to any great extent, the material is beingrolled too wet for the equipment being used; at opti-mum water content it may be expected that a fewclods will be picked up by the roller but a general stick-ing will not occur. If the compacted fill does not def-initely spring (noticeable to visual observation) underhauling and compaction equipment, it is probable thatseveral lifts of fill have been placed too dry. The rollershould roll evenly over the surface of the backfill if wa-ter content is uniform throughout the lift and shouldnot ride higher on some portions of the backfill thanon others. If on the first pass of a rubber-tired rollerthe tires sink to a depth equal to or greater than one-half the tire width, if after several passes the soil isrutting excessively, or if at any time during rolling theweaving or undulating (as opposed to normal “spring-ing” of the surface) of the material is taking placeahead of the roller, either the tire pressure is too highor the water content of the material is too high. On theother hand, if the roller tracks only very slightly or notat all and leaves the surface hard and stiff after sev-eral passes, the soil is probably too dry. For most soilshaving proper water contents, the roller will trackevenly on the first pass and the wheels will embed 3 to4 inches. Some penetration should be made into soil atits proper water content, though the penetration willdecrease as the number of passes increases. After sev-era1 passes of a sheepsfoot roller, the roller shouldstart walking out if adequate and efficient compaction

TM 5-818-4/AFM 88-5, Chap. 5

is being obtained. Walking out means the roller beginsbearing on the soil through its feet only-the drum isriding a few inches above the soil surface. If the rollerwalks out after only a few passes, the soil is probablytoo dry; if it does not walk out but continues churningup the material after the desired number of passes, thesoil is too wet or the foot contact pressure is too high.

(b) A trained inspector will spend some time inthe field laboratory, performing several compactiontests on each type of backfill material to become famil-iar with the differences in looks, feel, and behaviorand learning to recognize when they are too dry or toowet, as well as when they are at optimum water con-tent.

(2) Indirect methods. Indirect methods of deter-mining the density and water content involve meas-urement of the characteristic of the material that hasbeen previously correlated to the maximum densityand optimum water content. These methods of meas-uring in-place density and water content can usuallyeffect a more detailed control of a job than can be ac-complished by direct methods alone because they canprovide quicker determinations. However, no indirectmethod should ever be used without first checking andcalibrating it with results obtained from direct meth-ods, and periodic checks by direct methods should bemade during construction. Indirect methods includethe use of the nuclear moisture-density meter, theProctor penetrometer (often referred to as the “Proc-tor needle"), the hand cone penetrometer, and in thehands of an experienced inspector even a shovel.

(a) The nuclear moisture-density method con-ducted in accordance with ASTM D 2922 (for densitydetermination) and ASTM D 3017 (for water contentdetermination) is the only indirect control methodused for the Corps quality acceptance control. Themethod provides a relatively rapid means for deter-mining both moisture content and density. Of thethree methods presented in ASTM D 2922, Method B- Direct Transmission is the best suited for a com-pacted lift thickness exceeding approximately 4inches. The nuclear moisture-density method is dis-cussed in more detail in section B- 3, appendix B.

(b) Penetrometers, such as the Proctor and handcone penetrometers, are useful under certain condi-tions for approximating density. However, both meth-ods require careful calibration using soils of knowndensity and water content and considerable operatingexperience. Even then, the results may be questionablebecause nonuniform water content (in fine-grainedmaterial) or a small piece of gravel can affect the pene-tration resistance. Penetrometers, therefore, are notrecommended for general use in compaction control;however, they can be a very useful tool in supplement-ing the inspector’s visual observations and providing ageneral guide for detecting areas of doubtful compac-

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TM 5-818-4/AFM 88-5, Chap. 5

tion. The procedure using the Proctor penetrometerfor determining the relation between wet density,penetration resistance, and water content is describedin ASTM D 1558 and in section B-3, appendix B. Thehand cone penetrometer procedure also is discussed insection B-3.

(c) Many inspectors in the past have had goodsuccess in estimating density by simply observing theresistance of the compacted soil to penetration by aspade. This method requires considerable experienceand is useful only in detecting areas that might requirefurther density tests.

(3) Direct methods. Direct field density deter-mination consists of volume and weight measurementsto determine the wet density of in-place backfill andwater content measurements to determine in-place wa-ter contents and dry densities. The three methods usedfor the Corps quality acceptance density determina-tion are: (a) the sand-cone method according toMIL-STD-621 (Method 106) and ASTM D 1556;(b) the rubber-balloon method according to ASTM D2167; and for soft, fine-grained cohesive soils, thedrive-cylinder method according to MIL-STD-621(Method 102) and ASTM D 2937. In addition to the ap-proved methods, a method sometimes employed tomeasure densities of coarse-grained cohesionless mate-rial consists of the large-scale, water-displacementmethod. The large-scale, water-displacement methodis discussed in EM 1110-2-1911. The sand conemethod is considered to be the most reliable methodand is recommended as the proof or calibration test forcalibrating other methods such as the nuclear densitymethod. The direct field density methods are discussedin section B-3, appendix B.

e. Water content by microwave oven. The biggestproblem associated with both field compaction testsand in-place density and water content control tests isthe length of time required to determine water con-tent. Conventional ovendrying methods require from15 to 16 hours for most fine-grained cohesive soils. Insome cases, such as confined zones, the contractor mayhave placed and compacted several layers of backfillover the layer for which density tests were made be-fore quality acceptance test data are available. Eventhough the contractor places successive layers at hisown risk, a rapid turn around between testing and testresults could prevent costly-tear out and recompactprocedures. Drying specimens in microwave ovens of-fers a practical means for rapid determination of wa-ter content for most backfill materials if properly con-ducted. Times required for drying in a microwave ovenare primarily governed by the mass of water present inthe specimen and the power-load output of the oven.Therefore, drying time must be calibrated with respectto water content and oven output. Also, it may not bepossible to successfully dry certain soils containing

7-6

gypsum or highly metallic soils such as iron ore, alu-minum rich soils, and bauxite. Details of the micro-wave-oven method used for rapid determination of soilwater content is given in section B-3, appendix B.

f. Frequency and location of quality acceptancedensity tests. Acceptance control testing should bemore frequent at the start of backfill placement. Aftercompaction effort requirements have been firmly es-tablished and inspection personnel have become famil-iar with materials behavior and acceptable compactionprocedures, the amount of testing can be reduced.Many factors influence the frequency and location oftests. The frequency will be dependent on the type ofmaterial, adequacy of the compaction procedures, andhow critical the backfill being compacted is in relationto the performance of the structure.

(1) A systematic testing program should be estab-lished at the beginning of the job. Acceptance controltests laid out in a predetermined manner are usuallydesignated as routine control tests and are performedeither at designated locations or at random representa-tive locations, no matter how smoothly the compactionoperations are being carried out. A routine acceptancecontrol test should be conducted for at least every 200cubic yards of compacted backfill material in criticalareas where settlement of backfill may lead to struc-tural distress and for at least every 500 cubic yards inopen areas not adjacent to structures.

(2) In addition to routine acceptance control tests,tests should be made in the following areas: where theinspector has reason to doubt the adequacy of the com-paction; where the contractor is concentrating filloperations over relatively small areas; where smallcompaction equipment is being used such as in con-fined areas; and where field instrumentation is in-stalled, mainly around riser pipes.

g. Errors in field density measurements. Densityand water content measurements determined by anyof the methods discussed above are subject to threepossible sources of errors. The three categories ofpossible error sources are human errors, errors asso-ciated with equipment and method, and errors attrib-uted to material property behavior.

(1) Human error includes such factors as improperequipment readings and following improper test pro-cedures. Human errors are not quantitative. However,errors of this type may be minimized by utilizing com-petent testing personnel familiar with testing proce-dures.

(2) There are two types of possible errors relatedto test equipment. One type of error relates to thesensitivity of the equipment with respect to its capa-bility to accurately measure the true density or watercontent. Sensitivity errors are quantitative only in thesense that limiting ranges of possible error can be es-

TM 5-818-4/AFM 88-5, Chap. 5

quire separate analysis for each backfill material typeand compaction effort, complete random selection oftest locations, and a large number of control tests ascompared with the conventional decision method. Inaddition, statistical methods include water contentcontrol, which is not normally included in militaryspecifications.

(2) The theory and details concerning the applica-tion of statistical methods for compaction control arewell developed. Figure 7-1 shows a sequential inspec-tion plan example of how the end results of a statis-tical analysis might be used for the purpose of accep-tance or rejection. In this example, it was establishedby statistical analysis that adequate densities couldprobably be obtained with reasonable confidence by agiven compaction effort for desired water contentsranging from 3 percentage points below to 1 per-centage point above optimum. It was also establishedthat a density corresponding to 95 percent of CE 55maximum dry density was the minimum acceptabledensity based on required engineering performance ofthe backfill. The sequential inspection plan consists ofexamining, in sequence, single tests that are obtainedat random from a segment of the backfill being consid-ered for acceptance or rejection and, for each test,making one of three possible decisions: the segment isacceptable; the segment is unacceptable; and the evi-dence is not sufficient for either decision without toogreat a risk of error as indicated by the retest block infigure 7-1(a). The reject areas in figure 7-1 indicateconditions that cannot be corrected by additional roll-ing. The material must be replaced in thinner lifts andbe within the desired water content range before ade-quate compaction can be achieved with the compactionequipment being used. If the retest decision is reached,an additional test is made at a second random location,and the same three decisions are reconsidered in lightof this additional information. If the second test fallsbelow the accept blocks, the segment of backfill repre-sentative of that test should be rejected; or if compac-tion procedures that have produced acceptable tests inthe past have not been altered, then the compactioncharacteristics of that part of the backfill should be re-evaluated.

(3) The primary advantage of statistical methodsis that they offer a means of systematically evaluatingacceptance or rejection decisions rather than leavingsuch decisions entirely to the judgment of the inspec-tion personnel. However, if experienced and welltrained inspection personnel are available, this ap-proach may not be necessary.

tablished. An example of sensitivity error would be thenuclear density device that is capable of determiningdensities only to within 3 to 5 pounds per cubic foot oftrue density. The second type of error relates toconstant deviations between measured and true densi-ty. Constant deviation errors can be corrected by cali-brating test equipment against known densities.

(3) Material property errors are primarily limitedto density determinations using either the sand-coneor the rubber-balloon method in sands. When a soil isphysically sampled during the process of conductingan in-place density measurement using these twomethods, a shearing action of the soil is unavoidable.Cohesionless soils are sensitive to volume changeduring shear, dense sands tend to expand and increasein volume, and loose sands tend to contract and de-crease in volume. Errors of this nature cannot bequantified or detected in the field. However, sucherrors can be as high as 6 percent for sand using therubber-balloon method for volume measurements.

h. Acceptance or rejection. The inspection person-nel have the responsibility to accept or reject the back-fill or any part thereof based on the quality acceptancecontrol tests. On the surface, this task seems straight-forward. If a segment of the backfill tested at severallocations for acceptance passes or fails to pass mini-

mum requirements by a wide margin, then it is gener-ally safe to assume that the backfill within that seg-ment either has or has not been adequately compactedand the acceptance or rejection of that segment can bemade based on the test results. On the other hand, ifthe tests indicated insufficient compaction, the size ofthe affected area may be questionable; it is possiblethat the test(s) represents only a small area and the liftbeing tested may be sufficiently compacted elsewhere.In view of the possible errors associated with controltests, tests that indicate marginal passage or failureshould be treated with caution. The borderline case re-quires a close look at several factors: how the resultcompares with all previous results on the job, howmuch compaction effort was used and did it differfrom previous efforts, how does this particular mate-rial compare with previously compacted materials, theimportance of the lift location in relation to the entirestructure, and the importance of obtaining the correctdensity or water content from the designer’s stand-point. When all factors have been considered, a deci-sion is made as to which corrective measures are re-quired. What makes such decisions so difficult is thatthey must be made immediately; time will not permitthe problem to be pondered. Discussion with designengineers prior to beginning compaction operationsmay help in the evaluation of many of these factors.

(1) On jobs requiring large volumes of backfill, itmay be advantageous to base the decision to accept orreject on statistical methods. Statistical methods re-

i. Construction reports. A record should be main-tained of construction operations. It is valuable in theevent repairs or modifications of the structure are re-quired at a later time. A record is necessary in theevent claims are made either by the contractor or the

7-7

TM 5-818-4/AFM 88-5, Chap. 5

a. USE FOR INITIAL TEST OF BACKFILL b. USE FOR RETEST OF BACKFILLAT RANDOM LOCATION AT RANDOM LOCATION

NOTE: 95=SPECIFIED MINIMUM ACCEPTABLE PERCENTOF CE 55 MAXIMUM DRY DENSITY

Figure 7-1. Acceptance Rejection Scheme for a Backfill Area.

Contracting Officer that work required or performed portance of their reports and the need for thoroughwas not in accordance with the contract. Recorded reporting. Records should be made on every test per-data are also beneficial in improving knowledge and formed in the laboratory and in the field. All informa-practices for future work. The basic documents of the tion necessary to clearly define the locations at whichconstruction record are the plans and specifications, field tests are made should be presented. In the dailymodifications adopted that were considered to come reports, inspection personnel should include informa-within the terms of the contract, amendments to the tion concerning progress, adequacy of the work per-contract such as extra work orders or orders for formed, and retesting of areas requiring additionalchange, results of tests, and measurements of work work to meet specifications. These daily reports couldperformed. The amount of reporting required varies be of vital importance in subsequent actions. It is goodaccording to the importance and magnitude of the practice for the inspection personnel to keep a dailyearthwork construction phase of the project and the diary in which are recorded the work area, work ac-degree of available engineering supervision. The forms complished, test results, weather conditions, pertinentto be used should be carefully planned in advance, and conversations with the contractor, and instructions re-the inspection personnel should be apprised of the im- ceived and given.

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TM 5-818-4/AFM 88-5, Chap. 5

APPENDIX A

REFERENCES

Government PublicationsDepartment of Defense

Military StandardsMIL-STD-619 Unified Soil Classification System for Roads, Airfields, Embankments,

and Foundations.

MIL-STD-621 Test Methods for Pavement Subgrade, Subbase, and Base Course Mate-rials

Department of the Army, the Navy, and the Air Force

Technical ManualsAFM 89-3, Chapter 2TM 5-818-1/AFM 88-3, Chap. 7

TM 5-818-2/AFM 88-6,Chap. 4

TM 5-818-5/NAVFAC P-418/AFM 88-5, Chap. 6

TM 5-818-6TM 5-820-2/AFM 88-5, Chap. 2TM 5-820-4/AFM 88-5, Chap. 4NAVFAC DM-7

Materials TestingSoils and Geology: Procedures for Foundation Design of Buildings and

Other Structures (Except Hydraulic Structures)Pavement Design for Frost ConditionDewatering and Groundwater Control for Deep Excavations

Grouting Methods and EquipmentSubsurface Drainage Facilities for AirfieldsDrainage for Areas Other Than AirfieldsSoil Mechanics, Foundations, and Earth Structures

Department of the Army, Corps of Engineers

USACE Publications Depot, 809South Pickett, Alexandria, VA22304

EM 385-l-l Safety and Health Requirements Manual

EM 1110-2-1906 Laboratory Soils Testing

Em 1110-2-1908 Instrumentation for Earth and Rockfill Dams

EM 1110-2-1911 Construction Control for Earth and Rockfill Dams

EM 1110-2-2502 Retaining Walls

EM 1110-2-2902 Conduits, Culverts, and Pipes

ER 1110-2-1806 Earthquake Design and Analysis for Corps of Engineers Dams

Department of Interior

Bureau of Reclamation, Manual, Earth ManualSecond Edition

Department of Transportation (DOT) 1920 L Street, N.W., Washington, DC 20036

Report No. FHWA-RD-78-141 Design and Construction of Compacted Shale Embankments, Vol 5. Tech-nical Guidelines (December 1978)

A - l

TM 6-818-4/AFM 88-5, Chap. 5

Report No. FHWA-RD-79-51 Technical Guidelines for Expansive Soils in Highway Subgrades (June1979)

Non-Government Publications

American Society for Testing and Materials; 1916 Race Street, Philadelphia, PA 19103

D 1556

D 1557

D 1558

D 2049D 2167

D 2216D 2922

D 2937

D 3017

Special Technical PublicationSTP No. 293

Special Technical PublicationSTP No. 479

Special Technical PublicationSTP No. 599

Standard Test Method for Density of Soil in Place by the Sand-Cone Meth-od

Standard Test Methods for Moisture-Density Relations of Soils Using 10-lb (4.5 kg) Rammer and 18-in. (457-mm) Drop

Standard Test Method for Moisture-Penetration Resistance Relations ofFine-Grained Soils

Standard Test Method for Relative Density of Cohesionless SoilsStandard Test Method for Density of Soil In Place by the Rubber-Balloon

MethodStandard Method of Laboratory Determination of Moisture ContentStandard Test Method for Density of Soil and Soil-Aggregate In Place by

the Nuclear MethodsStandard Test Method for Density of Soil In Place by the Drive-Cylinder

MethodStandard Test Method for Moisture Content of Soil and Soil-Aggregate In

Place by the Nuclear MethodsSymposium on Nuclear Methods for Measuring Soil Density and Moisture

(June 1960)Special Procedures for Testing Soil and Rock for Engineering Purposes

(June 1970)Soil Specimen Preparation for Laboratory Testing (June 1976)

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TM 5-818-4/AFM 88-5, Chap. 5

APPENDIX B

FUNDAMENTALS OF COMPACTION, FIELD COMPACTION TEST METHODS,

AND FIELD MOISTURE-DENSITY TEST METHODS

Section B-1. FUNDAMENTALS OF COMPACTION

B-1. Factors influencing compaction. Soilcompaction is the act of increasing the density (unitweight) of the soil by manipulation by pressing, ram-ming, or vibrating the soil particles into a closer stateof contact. The most important factors in soil compac-tion are type of soil, water content, compaction effort,and lift thickness. It is the purpose of field inspectionto ensure that the proper water content, lift thickness,and compaction effort are used for each soil type sothat the desired degree of compaction is obtained.When the water content, lift thickness, or compactioneffort being used does not produce the desired degreeof compaction, changes may be necessary. The deter-mination of the necessary changes of these factors toproduce the desired degree of compaction requiresknowledge of the principles governing the compactionof soils. Therefore, it is important that inspection per-sonnel have a general understanding of the fundamen-tals of compaction.

a. General. It has been established through researchand construction experience that there is a maximumdensity to which a given soil can be compacted using aparticular compaction effect, For each soil and a givencompaction effort, there is a unique water content,which is called the optimum water content, that pro-duces the maximum density. The purpose of the laboratory compaction test is to determine the variationin density of a given soil at different water contentswhen compacted at a particular effort or efforts. Nor-mally, the soil to be used is compacted in the labora-tory over a range of water contents using the impact-compaction procedures given in MIL-STD-621A andASTM D 1557. The compaction effort used is selectedon the basis of the requirements of the structure. Infoundation or backfill design for most major struc-tures, the CE 55 (also termed modified) compaction ef-fort that produces approximately 56,000 foot-poundsper cubic foot of compacted soil should be used.

(1) For some cohesionless soils, a greater maxi-mum density can be obtained using vibratory-typecompaction procedures given in EM 1110-2-1906 andASTM D 2049 than can be obtained usingMIL-STD-621A or ASTM D 1557 impact-compactionprocedure. Thus, there may be cases where the vibra-

tory compaction method may be more appropriate indetermining the maximum density. The compactioneffort used for design purposes should be the basis forconstruction control.

(2) A compaction curve is developed in the impact-compaction test by plotting densities (dry unitweights) as ordinates and the corresponding watercontents (as percent of dry soil weight) as abscissas.For most soils the curve produced is generally para-bolic in form. Figure B-1 shows a compaction curve.The water content corresponding to the peak of thecurve is the optimum water content. The dry unitweight of the soil at the optimum water content is themaximum dry density. The zero air voids curve repre-sents the relation between water content and dry den-sity for 100 percent saturation of the particular mate-rial tested. Thus, it shows the dry density for a givenwater content based on the condition that all the air isforced out of the voids by the compaction process.

b. Influence of soil type. Compaction characteristicsvary considerably with the type of soil. Figure B-2shows four compaction curves representing the watercontent-density relation for four general soil types forstandard compaction. The maximum dry density for auniform sand occurs at about zero water content, al-though density approaching maximum can be obtainedwhen the sand is saturated. A very sharp peaked curveof dry density versus water content is usually obtainedfor a silt, and water content is critical to achievingmaximum density. A small change in water content (assmall as 0.5 percentage point) above or below optimumcauses a significant decrease in the density (as much as2 to 4 pounds per cubic foot) for a given compaction ef-fort. The compaction curve for a lean clay is not assharp as that for the silt, and water content control isnot as critical. Optimum water contents for silts andlean clays generally range between 15 and 20 percent.The compaction curve for fat clays is rather flat andwater content is not particularly critical to obtainingmaximum density; a 2 to 3 percentage point change inwater content from optimum for fat clays causes onlya small decrease (1 pound per cubic foot or less) in den-sity. The maximum dry density, as obtained in labora-tory compaction tests using MIL-STD-621A and

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TM 5-818-4/AFM 88-5, Chap. 5

Figure B-1. Compaction curve.

Figure B-2. Typical compaction test curves.

ASTM D 1557 or modified compaction effort, dependson the soil type and varies generally from about 125 to140 pounds per cubic foot for well-graded, sand-gravelmixtures to about 90 to 115 pounds per cubic foot forfat clays. The optimum water content generally rangesfrom zero for the sand-gravel mixtures to about 30 per-cent for the fat clays.

c. Influence of water content. For a given fine-grained soil and a given compaction effort, the watercontent determines the state at which maximum drydensity occurs. At low water contents when the soil is

stiff and hard to compress, low, dry densities and highvalues of air content result. As the water content is in-creased, higher dry densities and lower air contentvalues are obtained. Increased densities result with anincrease in water content up to optimum water con-tent. Beyond this point, the water in the voids becomesexcessive, and pore pressures develop under the appli-cation of the compaction effort to resist a closer pack-ing; lower dry densities are the result.

d. Influence of compaction effort. For most soils, in-creasing the energy applied (compaction effort) perunit volume of soil results in an increase in the maxi-mum density (unit weight). This greater density occursgenerally at a lower water content. This phenomenonis evident in both field and laboratory compactions.Thus, for each compaction effort, there is a unique op-timum water content and maximum dry density for agiven soil. Figure B-3 shows the effect of variation incompaction effort on the maximum dry density andoptimum water content for a lean clay (CL). Wherevalues of maximum dry density and optimum watercontent are specified, they should be referenced to thecompaction effort used.

e. Influence of lift thickness. Compaction effort ap-plied to a soil surface dissipates with depth. Therefore,it is important that the lift thickness to be compactedbe commensurate with the type of soil and the compac-tion effort. With proper consideration and control overfactors influencing compaction, most soils can be com-

Figure B-3. Molding water content versus density-lean clay (labora-tory impact compaction).

B-2

pacted to provide a stable backfill, with the exceptionof certain bouldery soils and soils containing signifi-cant amounts of soluble, soft, or organic materials.

B-2. Mechanics of compaction. The influ-ence of the water content on compaction is markedlydifferent on coarse-grained, cohesionless soils andfine-grained, cohesive soils. As a result, the mechanicsor manipulation of soil grains in the two types of soilduring the compaction process are different. Themechanics of compaction for the two soil types are dis-cussed in subsequent paragraphs.

a. Compaction of coarse-grained soils. Compactionof coarse-grained soils that contain little or no finesand thus exhibit no plasticity (termed cohesionlesssoils) is achieved by causing the individual particles tomove into a closer, more compact arrangement, withsmaller particles filling in voids between larger parti-cles. The compaction energy overcomes friction at con-tact points between particles as they move past one an-other into closer packing.

(1) A loose volume of coarse-grained soil, such asgravel or sand, contains spaces or “voids” between in-dividual particles that are filled with air and/or water.The density that can be obtained in such a soil under agiven amount of compaction effort depends on thegradation and shapes of the particles and on the watercontent. For a well-graded gravel or sand, the range ofparticle sizes is sufficient to allow a fairly compact ar-rangement of particles, with smaller particles filling inthe voids between larger particles. For poorly gradedsoil, either of uniform gradation or skip-graded (lack-ing a specific range of particle sizes), the distributionof particle sizes limits the density that can be ob-tained. Segregation of similar size particles in a skip-graded material tends to occur and prevents the voidsfrom being greatly reduced. In a uniform soil, point-to-point contact occurs at very low compaction effort andlow density results; further increase in density canonly be accomplished by crushing the grains. There-fore, a well-graded, coarse-grained material can gener-ally be compacted to a greater density under a givencompaction effort than a poorly graded, coarse-grained soil. The increase in maximum density with in-crease in compaction effort will be greater for a well-graded soil than that for a poorly graded soil.

(2) Rounded particle shapes facilitate movementand sliding of particles, while angular particle shapesrestrict movement and sliding of grains in relation toone another. For either a well-graded, or a poorly grad-ed, coarse-grained material, increase in angularily ofgrains requires a corresponding increase in compac-tion effort to obtain a given density. However, a high-er density can usually be attained with angular soilsbecause the particle shapes are more conducive to fill-ing the voids.

TM 5-818-4/AFM 88-5, Chap.5

(3) For coarse-grained soils containing only asmall percentage (5 or less) of fine-grained particles,maximum density is more readily obtained when thesoil is either dry or saturated. For water contents be-tween these limits, the water in the soil forms meniscibetween the particle contacts, which tend to hold thesoil particles together. This resistance to movement ofparticles into a more compact structure, termed appar-ent cohesion or “bulking,” results in lower densitiesthan those for either a dry or saturated cohesionlesssoil under the same compaction effort.

(4) It is to be noted that in the preceding para-graphs, the discussion has centered around the densityin weight per unit volume of coarse-grained soils withdifferent gradation characteristics. A more realisticparameter that is often used is the relative density ofcohesionless coarse-grained soils. Relative density ex-presses the degree of compactness of a cohesionlesssoil with respect to the loosest and the densest condi-tions of the soil that can be attained by specifiedlaboratory procedures. A soil in the loosest state wouldhave a relative density of zero percent and in the dens-est state, a relative density of 100 percent. The dryunit weight of a cohesionless soil does not, by itself, re-veal how loose or how dense the soil is due to the influ-ence of particle shape and gradation on the density.Only when viewed against the possible range of varia-tion, in terms of relative density, can the dry unitweight be related to the compaction effort used toplace the soil in a backfill or indicate the volume-change tendency of the soil when subjected to founda-tion loads.

(5) Most coarse-grained soils can be compacted toa density such that detrimental additional consolida-tion will not take place under the prototype loading.This factor is the first important consideration. An-other important consideration may be that the com-pacted soil be sufficiently pervious to provide gooddrainage. Proper consideration of these two basicfactors will allow the use of most coarse-grained soilsfor backfill purposes.

b. Compaction of fine-grained soils. The mechanicsby which fine-grained soils are compacted is quite com-plex because capillary pressures, hysteresis, pore airpressure, pore water pressure, permeability, surfacephenomena, osmotic pressures, and the concepts of ef-fective stress, shear strength, and compressibility areinvolved. Numerous theories have been developed inan attempt to explain the compaction mechanics. Thecurrent state-of-the-art theories involving effectivestress give satisfactory explanations. The basic con-cepts of these theories are discussed below.

(1) Fine-grained soils are compacted in a partiallysaturated state; therefore, voids or pores contain bothpore air and pore water between the soil particles. Ini-

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TM 5-818-4/AFM 88-5, Chap. 5

tial compaction water contents below optimum resultin initial high pore air pressures and pore water pres-sures, which reduce shear strength and allow soilparticles to slide over one another displacing the poreair to form a more dense mass. This process continuesas long as the trapped pore air pressure can escape butrequires increasing amounts of compaction effort toachieve higher densities since the soil particles carryincreasing amounts of the compaction energy. For agiven compaction effort, enough water may eventuallybe added to the soil so that air channels become discon-tinuous, and the air is trapped. When the air voids be-come completely discontinuous, the air permeability ofthe soil drops to zero; no further densification is possi-ble because at this condition transient pore air pres-sures can develop that resist the compaction effort. Atzero permeability the soil has reached its so-called“optimum water content.” Since zero permeability may

also be established by closer packing of soil particles, itis evident that lower optimum water contents are pos-sible at higher compaction efforts.

(2) The addition of water above optimum watercontent causes the voids to become completely filledwith trapped pore air and pore water and thereby pre-vents the soil particles from moving into a more com-pact arrangement no matter what the compaction ef-fort. Pore water pressure increases significantly withincreasing water contents and causes increased reduc-tion in shear strength. This fact is evident in thelaboratory compaction mold when the compaction footsinks deeper and deeper into the soil as water contentincreases past optimum. The same process occurs inthe field when sheepsfoot rollers sink into the soil un-til the weight is carried by the drum or excessive rut-ting with rubber-tired rollers.

Section B-2. FIELD COMPACTION TEST METHODS

B-3. General. Laboratory test data obtained fromlaboratory-compacted specimens provide a basis fordesign, and it is assumed that the engineering charac-teristics that will be built into the field-compactedbackfill will be approximately the same as those of thespecimens. Experience has indicated that for mostsoils, laboratory densities, water contents, andstrength characteristics can be satisfactorily repro-duced in a field-compacted backfill.

B-4. Field compaction tests.a. Compaction control tests. Compaction control of

soils requires comparison of fill water content and drydensity values obtained in field density tests with opti-mum water content and maximum dry density, or de-termination of relative density if more appropriate forthe fill materials that are cohesionless. For fine-grained or coarse-grained soils with appreciable fines,field results are compared with results of CE 55laboratory (modified effort) compaction tests per-formed according to procedures presented inMIL-STD-621A and ASTM D 1557. For free-drainingcohesionless soils, relative density of the fill materialis determined, if appropriate, using vibratory test pro-cedures prescribed in EM 1110-2-1906 and ASTM D2049.

b. Frequency compaction control tests. The per-formance of a standard laboratory compaction test onmaterial from each field density test would give themost accurate relation of the in-place material to opti-mum water content and maximum density, but thistest is not generally feasible to do because testingcould not keep pace with the rate of fill placement.However, standard compaction tests should be per-formed during construction (1) when an insufficient

B-4

number of the compaction curves were developed dur-ing the design phase, (2) when borrow material is ob-tained from a new source, and (3) when material simi-lar to that being placed has not been tested previously.In any event, laboratory compaction tests should beperformed periodically on each type of fill material(preferably 1 test for every 10 field density tests) tocheck the optimum water content and maximum drydensity values being used for correlation with fielddensity test results.

c. Quick field compaction tests. In addition to thestandard compaction or relative density tests (paraB-2a), at least four relatively quick compaction testmethods can provide good approximations of maxi-mum dry density comparable to the standard methods.The quick compaction methods include: one-point andtwo-point compaction methods; the Water and PowerResource Service (WPRS), formerly U.S. Bureau ofReclamation (USBR) rapid compaction controlmethod; and for granular cohesionless material, com-paction control by gradation. Since only the one-pointand two-point methods are currently accepted by theCorps of Engineers for compaction control tests, onlythese two methods will be discussed in detail. TheUSBR and gradation methods are briefly summarized.

(1) One-point compaction method. In the one-point compaction method, material from the fielddensity test is allowed to dry with thorough mixing toobtain a uniform water content on the dry side of esti-mated optimum, and then compacted using the sameequipment and procedure used in the five-point stand-ard compaction test. The water content and dry densi-ty of the compacted sample are then used to estimateits optimum water content and maximum dry densityas illustrated in figure B-4. The line of optimums is

well defined in the figure, and the compaction curvesare approximately parallel to each other; consequent-ly, the one-point compaction method could be usedwith a relatively high degree of confidence. In figureB-5, however, the optimums do not define a line, but abroad band. Also, the compaction curves are not paral-lel to each other and in several instances cross on thedry side. To illustrate the error that could result fromusing the one-point method, consider the field densityand water content shown by point B in figure B-5.Point B is close to three compaction curves. Conse-quently, the correct curve cannot be determined fromthe one point. The estimated maximum dry densityand optimum water content could vary from about92.8 pounds per cubic foot and 26 percent, respective-ly, to 95.0 pounds per cubic foot and 24 percent, re-spectively, depending on which curve was used. There-fore, the one-point method should be used only whenthe basic compaction curves define a relatively goodline of optimums.

Figure B-4. Illustration of one-point compaction method.

(2) Two-point compaction test results. In the two-point test, one sample of material from the location ofthe field density test is compacted at the fill water con-tent if thought to be at or on the dry side of optimumwater content (otherwise, reduced by drying to thiscondition) using the same equipment and proceduresused in the five-point compaction test. A second sam-ple of material is allowed to dry back about 2 to 3 per-centage points dry of the water content of the firstsample, and then compacted in the same manner. Af-ter compaction, water contents of the two samples aredetermined by ovendrying or other more rapid means

TM 5-818-4/AFM 88-5, Chap. 5

Figure B-5. Illustration of possible error using one- and two-pointcompaction methods.

(para B-8a), and dry densities are computed. The re-sults are used to identify the appropriate compactioncurve for the material test (fig. B-6). The data shownin figure B-6 warrant the use of the two-point compac-tion test since the five-point compaction curves are notparallel. Using point A only as in the one-point testmethod would result in appreciable error as the shapeof the curve would not be defined. The estimated com-paction curve can be more accurately defined by twocompaction points as shown. Although the two-pointmethod is more accurate than the one-point method,neither method would have acceptable accuracy whenapplied to the set of compaction curves shown infigure B-5.

(3) Rapid one-point test for sands. A rapid checktest for compaction of uniform sands (SP to SM) withless than 10 percent fines (minus No. 200 sieve) is amodified one-point test. The ovendry sand is com-pacted in a 4-inch-diameter mold using CE 55 (modi-fied) effort. Correlation with standard compactiontests is required to confirm the validity of test resultsfor different sands used on each project.

(4) USBR rapid compaction control method. De-tails of this method are described in the USBR EarthManual (app A), The test is applicable to fine-grained(100 percent minus No. 4 sieve) cohesive soils with li-quid limits less than 50. The method, however, is ap-plicable to soils containing oversize particles providingthe proper corrections, as stated in EM 1110-2-1911,Appendix B, are applied. It is a faster method than thestandard compaction test and is often more accuratethan other methods. The method usually requires add-ing water to or drying back sampled fill material, andthorough mixing is needed to obtain uniform drying or

B-6

TM 5-818-4/AFM 88-5, Chap. 5

Figure B-6. Illustration of two-point compaction method

distribution of added water. Otherwise, the resultsmay be erroneous, especially for highly plastic clays.In tough clays, it is likely to be inaccurate because ofinsufficient curing time for the specimens.

(5) Grain-size gradation compaction control meth-od. This test method developed in 1938 is applicable tocoarse, medium, and fine-grained sands. The methodinvolves sieve analysis to establish grain-size grada-tion curves, whose shapes are then correlated withmaximum dry density obtained from the standardfive-point compaction tests or relative density tests.For a given compaction effort, the maximum drydensity of cohesionless material (sand) is also a func-tion of particle shape. Thus, the correlation betweengrain-size distribution and density would, by necessity,have to include consideration of particle shape. It isdoubtful that this method would provide test resultsmore rapidly than the one-point and two-point meth-ods or the relative density method currently acceptedby the Corps since samples must be dried for sieveanalysis. Therefore, this method is not recommendedfor routine compaction control.

d. Possible errors. All tests involving mechanical de-vices and human judgment are subject to errors thatcould affect the results. In order to properly evaluatetest results, the inspector must be familiar with thepossible sources of such errors.

(1) Five-point compaction tests. The following er-rors can cause inaccurate results:

(a) Aggregations of air-dried soil not completelyreduced to finer particles during processing.

(b) Water not thoroughly absorbed into driedmaterial because of insufficient mixing and curingtime.

(c) Material reused after compaction.

B-6

(d) Insufficient number of tests to define com-paction curve accurately.

(e) Improper foundation for mold during com-paction.

(f) Incorrect volume or weight of compactionmold.

(g) Incorrect rammer weight and height of fall.(h) Excessive material extending into the exten-

sion collar at the end of compaction.(i) Improper or insufficient distribution of

blows over the soil surface.(j) Tendency to press the head of the rammer

against the specimen before letting the weight fall.(k) Insufficient drying of sample for water con-

tent determination.(2) One-point and two-point compaction test. The

possible sources of errors for the one-point and two-point compaction test are essentially the same as thosefor the five-point method discussed in (1) above. In ad-dition, appreciable inaccuracy in results may occur forboth methods if attempts are made to extrapolatemaximum density and optimum water contents fromnonuniform families of compaction curves (fig. B-5).

B-5. Field compaction and test sections.For most soils, laboratory densities, water contents,and strength characteristics can be satisfactorilyreproduced in a field-compacted backfill. However,during the initial stage of construction frequentchecks of density and water content should be madefor comparison with design requirements and adjust-ments should be made in the field compaction proce-dure as necessary to ensure adequate compaction.

a. When a compacted backfill is constructed asfoundation support for critical structures, or whenother requirements, materials, and conditions are un-usual, the specifications may provide for the construc-tion of test sections. The test section is used to deter-mine the best procedures for processing, placing, andcompacting the materials that will produce compactedbackfill having engineering properties compatiblewith design requirements. Therefore, construction of atest section may involve using different types and dif-ferent weights of compaction equipment, using differ-ent lift thicknesses, using different amounts of com-paction applications (different numbers of passes orcoverages), processing materials differently with re-spect to water content control, and mixing to obtainimproved gradation. A discussion on test sections forshale materials is presented in Appendix A ofFHWA-RD-78-141 and illustrates a wide variation intest results, even for very carefully conducted fieldtests.

b. By exercising rigid control over the water con-tent, processing, placement, and compaction proce-dures, by frequent density sampling, by keeping com-

TM 5-818-4/AFM 88-5, Chap. 5

not contained in the specifications, the field engineersand inspection personnel should provide maximumguidance to the contractor to aid him in establishingadequate processing, placement, and compaction pro-cedures. To meet this problem the contractor must beprovided with suggested improvements of equipmenttype, if they have not been specified, and proceduresduring the initial stages of backfill operations. The es-tablishment of the procedures and equipment typethat will produce adequate compaction of the backfillmaterial must be supported by a comprehensive pro-gram of control testing.

plete records of the procedures and tests, and then bystudying and evaluating these records, a procedure touse on the job can be established. In addition to watercontent and density check tests, undisturbed samplesshould be obtained to determine that the shear andconsolidation characteristics are consistent with de-sign requirements. Once control for field conditionshas been established, the backfill can proceed at a nor-mal rate. The contractor should be required to adhereto the established processing, placement, and compac-tion procedures.

c. If provisions for construction of a test section are

Section B-3. FIELD MOISTURE-DENSITY TEST METHODS

B-6. General. Field density measurements of thecompacted backfill are essential to ensure that backfillmeets the required design densities necessary for theproper functioning of the structure within that back-fill. Although water content requirements are not gen-erally specified in military specifications, the measure-ment and control of water content is important in ob-taining required densities. The four density measure-ment test methods used for the Corps record and con-tract acceptance enforcement are listed below.

a. The sand-cone method as described in MlL-STD-621A (Method 106) and ASTM D 1556.

b. The rubber-balloon method as described in ASTMD 2167.

c. The nuclear moisture-density method as de-scribed in ASTM D 2922 (for density) and ASTM D3017 (for water content).

d. The drive-cylinder method as described inMIL-STD-621A (Method 102) and ASTM D 2937 forsoft, fine-grained cohesive soils. The water-displace-ment method described in EM 1110-2-1911, althoughnot currently used for Corps contract enforcement,may be used for supplementary density testing forrocky materials. Rapid field methods of determiningor approximating water content-density are also dis-cussed in the following paragraphs.

B-7. Water content and density testmethods. Field density can be determined by director indirect methods. In the direct methods, the weightof soil removed from a hole and the volume of the holeare determined and used to compute the density. Inthe indirect methods, a characteristic of the soil, suchas radiation scattering or penetration resistance, ismeasured with an instrument such as a nuclear densi-ty meter or penetrometer, and then a previously deter-mined relation between density and the characteristicmeasured is used to determine the density.

a. Direct methods. The sand-displacement methodis considered to be the most reliable direct method and

should be used as the standard test by which indirecttest results are correlated with density. Other directmethods are the drive-cylinder method, rubber-balloonmethod, and water-displacement method.

(1) Sand-cone method. Procedures and equipmentfor the sand-cone method are described in MIL-STD-621A (Method 106) and ASTM D 1556. The pro-cedure as described in the references involves prepara-tion of the ground surface, measurement of an initialvolume for the purpose of correcting for surface ir-regularities, and measurement of a second volumeafter a small hole is dug. The difference in the volumesis the volume of the hole. The sand used is a standardsand (Ottawa or other sands having rounded grainsand a uniform gradation) that has been calibrated forweight versus volume occupied when falling from astandard, constant height. The weight of sand used ismeasured by weighing the sand density cylinder be-fore and after each volume measurement, and thevolume is determined from the weight versus volumecalibration. The soil removed from the hole is weighed,the water content determined (MIL-STD-621A), andthe dry weight computed. The wet density and drydensity of the soil are computed by dividing the appro-priate weights by the computed volume. The sand-conemethod can be used to determine the in-place densityof practically all soils except those containing largequantities of large gravel sizes.

(2) Drive-cylinder method. Procedures and equip-ment for the drive cylinder method are described in de-tail in MIL-STD-621A (Method 102) and ASTM D2937. The procedure consists of driving a 3-inch-diam-eter by 3-inch-high sampling tube of known volumeinto the soil, excavating the sampling tube and soil,and trimming off the soil protruding from the ends ofthe tube. The weight and water content of the soil aremeasured and the dry weight is computed. The wetdensity and dry density of the soil are computed bydividing the appropriate weights by the computedvolume. The drive-cylinder method is limited to moist,fine-grained cohesive soils.

B-7

TM 5-818-4/AFM 88-5, Chap. 5

(3) Rubber-balloon method. Procedures and equip-ment for the rubber-balloon method are described inASTM D 2167. This method utilizes a rubber balloonattached to a glass or metal cylinder containing waterand having a scale graduated in cubic feet. An annulardevice is seated on the prepared ground surface, andthe balloon apparatus is placed and held down firmlyon the ring. Then water is forced into the balloonunder pressures of 2 to 3 pounds per square inch to ob-tain an initial volume measurement to correct forground surface irregularities. The apparatus is re-moved, a small hole is dug, and the apparatus is re-placed on the ring. Water is again pumped into the bal-loon and causes the balloon to conform to theboundary of the hole; then the volume is measured.This volume less the initial volume is the volume of thehole. The volumeter apparatus is simple and easy tooperate, and the volume measurement can be made di-rectly and in somewhat less time than that with thesand-cone volume apparatus. The results obtained areconsidered to be as accurate as those obtained from thesand-cone apparatus. Like the sand-cone method, therubber-balloon method can be used to determine thein-place density of practically all soils except thosecontaining large quantities of large gravel sizes.

(4) Water-displacement method. Where it is nec-essary to determine the in-place density for a largevolume of soil, as in coarse-grained soils containingsignificant quantities of large gravel sizes, an approx-imate density can be obtained by excavating a largehole (several cubic feet) and determining the volumeby lining the hole with thin plastic sheeting and meas-uring the quantity of water required to fill the hole. Arelatively small sample representative of the materialfrom the excavation is used for determining the watercontent. Using the wet and dry weights of the materialexcavated and the measured volume of the hole, thewet and dry densities of the soil can be determined. Al-though the procedure is not contained in a MilitaryStandard, it is about the only means of determining anapproximate density for soils with large sizes of gravelor rock.

b. Size and preparation of test hole. The size of thehole and the care used in preparing the test hole forthe sand volume and balloon methods influence theaccuracy of the volume measurement. The proper sizeof the hole is not well established; however, the largerthe hole, the less significant small errors in measure-ment of volume become. The instructions in TM5-824-2 indicate that a volume of at least 0.05 cubicfoot should be used when testing materials with amaximum particle size of 1 inch and that larger vol-umes should be used for larger maximum particlesizes. ASTM D 1556 suggests certain relations be-tween particle size and the test hole volume andweight of water content specimen. It also recommends

B-8

increasing the size of the sample used for water con-tent determination with increasing maximum particlesize. The relations suggested by the American Societyfor Testing and Materials are shown in the followingtabulation:

Minimum test Water contentMaximum particle hole volume sample

size, in. cu ft0.187 (No. 4) 0.025 1001/2 0.050 2501 0.075 5002 0.100 1,000

For significant quantities of larger particles the vol-umes above should be doubled. The accuracy of the testresults is influenced by not only the care taken in pre-paring a test hole but also the degree of recovery of theexcavated material. A hole with irregular surfaces willcause the volume measurement to be less accuratethan a hole with smooth surfaces. Thus, the inside ofthe hole should be kept as free of pockets and sharpprojections as possible. Digging a smooth test hole incohesionless coarse-grained material is particularlydifficult. In fine-grained soils without gravel particles,the hole may be bored with an auger, but hand toolswill be required to smooth the walls and base of thehole and to recover loose material. For coarser-grainedsoils and soils containing a significant amount of grav-el-size particles, hand tools will generally be requiredto excavate the hole to prevent disturbing the materialin the walls and base of the test hole. Should it becomenecessary in digging a test hole in highly compactedmaterial to loosen the material by using a chisel andhammer, care must be taken not to disturb the soilaround the limits of the hole. All loose particles mustbe removed after the final depth has been reached, andall particles must be recovered. All soil should beplaced in a waterproof container as the soil is takenfrom the hole. This measure will prevent loss of waterbefore the soil can be weighed.

c. Indirect methods. The indirect methods includeuse of the nuclear moisture-density apparatus, Proctorpenetrometer, and cone penetrometer. Both the Proc-tor penetrometer and cone penetrometer methods fordetermining the density require very careful calibra-tion using soils of known density and water content,and considerable experience in operating the device;even so, the accuracy of these methods may be subjectto question because of the great influence that nonuni-formity of water content or a small piece of gravel canhave on the penetration resistance. The Proctor pene-trometer may also be used to approximate water con-tent of fine-grained soils.

(1) Nuclear moisture-density method. Proceduresand equipment for the nuclear moisture-density meth-od are described in ASTM D 2922 (for density) andASTM D 3017 (for water content). The three methodsfor determining in-place densities described in ASTM

D 2922 are Method A-Backscatter, Method B-DirectTransmission, and Method C-Air Gap. Of the threemethods, Method B-Direct Transmission is recom-mended over Method A and Method C because it elim-inates the effect of vertical density variations.

(a) Modern nuclear-moisture density equipmentincorporates a radioactive source emitting neutronsand gamma rays and measuring elements (geigertubes) or “scalers” into a single, self-contained unit.The determination of moisture by the nuclear methodis dependent on the modifying of high energy or “fast”neutrons into low energy or “slow” neutrons (ASTM,STP No. 293). Any material containing hydrogen willmoderate fast neutrons. Since hydrogen is present pri-marily in the molecules of free water, the degree ofinteraction between the fast neutrons and hydrogenatoms represents a measure of the water content of thesoil, Density measurements are based on the scatteringof gamma rays by the orbital electrons on the atomscomprising the soil. Since the scattering is a functionof the electron density, which in turn is approximatelyproportional to the density of the soil, it is possible tocorrelate the backscatter of the gamma rays with thesoil density.

(b) To obtain a water content or density meas-urement, the appropriate meter is set in place and thevoltage setting is adjusted to the correct operatingvoltage. After the scaler is turned on, a short warmupperiod (not exceeding 1 minute) is allowed before thetest count is started. Intimate contact at the interfacebetween meter and soil is necessary for Method A-Backscatter because the scattering of the gamma raysfor the density measurement is quite sensitive to evenminute air gaps. The normal counting period is 1minute, with one or two repeat counts taken as acheck. Calibration curves for both moisture and densi-ty determinations, once the count rates have been es-tablished, are furnished by the manufacturers for eachindividual unit. In general, the calibration curve formoisture determination is more reliable than the curvefor density determination. However, it is advisable tocorrelate both calibration curves on each type of soilwith which the instrument is to be used. Such a corre-lation should be accomplished by using current stand-ard methods for moisture and density determinationsor by calibrating on blocks of material of known mois-ture and density. Examples of calibration for shalematerials are given in Appendix A of FHWA-RD-78-141.

(c) For all nuclear-moisture density devices,separate standards are provided so that the count ratecan be determined on each instrument at any time inthe field. A standard count should be taken three orfour times during a day’s operation. Although adjust-ments can generally be made on the instruments sothat the count will coincide with the standard count;

TM 5-818-4/AFM 88-5, Chap. 5

even a slight adjustment is not usually justified. Amore satisfactory procedure is to record the fieldmeasurement in terms of percent of this standardcount rate, which should be within a reasonable per-centage ( ± 5) of the given reference count. Use of thepercent of standard count, rather than simply thecounts per minute, is recommended for increased accu-racy. Use of this procedure largely cancels out theeffects of such variables as reduction in sourcestrength, background count, and changes in sensitivityof the detector tubes.

(d) The calibration curve for the soil beingtested is entered with the value of the density metercount rate (taking into consideration the variationfrom the standard count) to obtain the wet unit weightof the soil. Similarly, the moisture meter yields theweight of water per cubic foot of soil. The unit dryweight of the soil is simply the wet unit weight ob-tained by the density meter minus the weight of waterobtained by the moisture meter. By dividing the watermeasurement by the dry density, the water contentcan be expressed in the more familiar terms of percent-age of dry weight.

(e) Anyone working with nuclear meters mustrecognize that a possibility of exposure to radiation ex-ists if the safety rules listed by the manufacturer arenot followed. When proper procedures and safety rulesare followed, the radiation hazard is negligible. Forcertain instruments, operating personnel must wear abody radiation film badge and carry a pocket dosim-eter. These instruments must be ready weekly to en-sure that the maximum permissible weekly dosage isless than 100 milliroentgen. Other safety rules dealwith handling the devices and being aware of the built-in safety devices. The safety precautions mentionedabove may vary or not be applicable for some of thenewer devices being manufactured. Therefore, themanufacturer’s literature should be carefully studied todetermine appropriate safety requirements.

(f) It is possible, using nuclear-moisture densityapparatus, for one inspector to conduct perhaps 30 wa-ter content and 30 density tests per 8-hour workingday. The time required per test is only 20 or 25 percentof that required in direct sampling methods. A largenumber of tests with the nuclear meter correlated witha much smaller number of direct sampling determina-tions can be of great benefit in ensuring that adequatecompaction of the backfill is being obtained. A simplestatistical analysis of the data can be made, such as aplot of dry density versus number of tests (ASTM STPNo. 293). The resulting bell-shaped curve is a very use-ful tool since each day’s results can easily be added tothe plot of previous test results. This procedure canprovide an up-to-date picture of the fill densities beingobtained and can show the effect of changes made infield compaction procedures.

B-9

TM 5-818-4/AFM 88-5, Chap. 5

(2) Hand cone penetrometer. The hand cone pene-trometer offers a rapid means of checking density re-quirement of some compacted backfills. The processinvolves the correlation of penetration resistance withknown in-place densities as determined by either thesand-cone or the rubber-balloon method.

(a) Cone penetration resistance is a measure-ment of soil bearing capacity. Since bearing capacity isdependent on shear strength and thus density, thehand cone penetrometer is an indirect measurement ofdensity. Because shear strength is a function of anypore air and pore water pressures that may be gener-ated by a shearing action of soils containing pore wa-ter, the method is applicable only to free-drainingmaterials where pore pressures are dissipated as fastas they are generated. Penetration resistance can alsobe drastically influenced by the obstruction of gravel-size particles. Therefore, the method is applicable onlyto sands with 100 percent passing the U.S. StandardNo. 4 sieve (4.76 mm) and no more than 15 percentpassing the U.S. Standard No. 200 sieve (0.074 mm).

(b) A plot of hand-cone sounding resistance ver-sus depth of sounding will result in an approximatelinear relationship for homogenous materials of rela-tively constant density for depths of sounding rangingfrom approximately 2 inches to 20 inches dependingon the geometry and size of the cone point and mate-rial type. Correlations may be made between knownin-place densities and either the angle of inclinationbetween sounding resistance and depth of penetrationor the sounding resistance at a given depth. The rangeof known in-place density must be sufficient to estab-lish a trend between sounding resistance and density.Correlations between density and sounding resistanceat a given depth is the simplest correlation since theangle of inclination does not have to be computed.Figure B-7 shows a case example of a correlation be-tween dry density and sounding resistance measuredat 6 inches below the surface. Contract specificationrequired a minimum acceptable dry density of 104.7pounds per cubic foot (98 percent of the maximum drydensity according to the compaction method describedin ASTM D 1557). Figure B-7 also indicates that allsoundings with resistances of 110 pounds or more cor-responded to densities greater than 104.6 pounds percubic foot. Therefore, no additional standard densitychecks are needed beyond the routine tests. When allsoundings with resistance of 86 pounds and below cor-respond to densities below 104.6 pounds per cubicfoot, it is evident that sufficient compaction has notbeen achieved and additional standard density checksare definitely needed for an acceptance or rejectiondecision. Sounding with resistances between 86 and110 pounds may or may not need additional densitychecks depending on whether the inspector has reason

B- 10

to suspectachieved.

adequate compaction has or has not been

Figure B-7. Correlation between dry density and hand cone resist-ance at a depth of 6 inches below the surface.

(c) The correlation between sounding resistanceand known in-place dry densities (fig. B-7) is made di-rectly without knowing water content at each sound-ing location. Although sounding resistances are af-fected by water content for the dry, moist, and 1 to 2percentage points above optimum state, the range ofpossible water content in the moist state does not sig-nificantly affect sounding resistance.

(d) The hand cone penetrometer is ideally suitedfor use in confined zones where sand is used as backfilland where rapid control aids are needed to determineif adequate compaction has been achieved. With a lit-tle practice, a hand-cone sounding can be -made in lessthan 1 minute.

d. Possible sources of errors. Since the decision toaccept or reject a particular part of a backfill is primar-ily dependent upon the results of in-place density con-trol tests, it is important for the inspector to be famil-iar with the possible sources of errors that might causean inaccurate test result. Some of the more likelysources of errors for the sand-cone, rubber-balloon,and nuclear moisture-density methods are discussedbelow. All tests that are suspected to be in error mustbe repeated.

(1) Sand-cone method. The major sources of possi-ble error are as follows:

(a) The sand-cone method relates the bulk den-sity of a standard sand to the known weight of the

TM 5-818-4/AFM 88-5, Chap. 5

tion curves may also be induced by differences in theseating, background count, sample heterogeneity, andsurface texture of the material being tested.

B-8. Rapid field water content controlprocedures. In many cases, particularly in con-fined zones, it is important to rapidly determine thedry density of a given part of the backfill in order toprevent the possibility of costly tear out and rebuildoperations. The test procedures for determining drydensities using the sand-cone and rubber-balloonmethods sometimes require extensive drying times(depend on material type up to 16 hours) to determinewater content. Alternate techniques for rapidly deter-mining water content are discussed below.

a. Microwave ovens. Microwave energy may be usedto dry soil rapidly and thus enable quick determinationof water content (ASTM STP No. 599). However, indrying soils with microwaves, the only control on theamount of energy absorbed by the soil is exposuretime; consequently, if soils are left in the oven toolong, severe overheating can occur. This overheatingof the soil can cause bound water, a part of the soilstructure, to be driven off and thus result in signifi-cant errors in water content measurements. In addi-tion, continuous heating can result in excessive heatbeing generated; certain soils have been observed tofuse or explode and thereby create hazards to bothequipment and personnel.

(1) Times required for drying in a microwave ovenare primarily governed by the mass of water presentand the power-load output of the oven, as expressed by

same sand occupying an in-place volume of sampledmaterial. Changes in effective gradation between orwithin batches of sand may significantly affect thetest results. This error can be minimized by frequentcalibration of the sand’s bulk density.

(b) Loose sand increases in density when sub-jected to vibrations. Care must be taken not to jar thesand container while calibrating bulk density in thelaboratory or during in-place volume measurements inthe field. A common error is to use the sand cone meth-od for in-place volume measurements adjacent to theoperation of heavy equipment. Heavy equipment cangenerate vibrations that densify the sand and result inerroneously high-volume measurements and low in-place densities.

(c) Appreciable time intervals between bulkdensity determination of the sand and its use in thefield may result in change in the bulk density causedby a change in the moisture content of the sand.

(2) Rubber-balloon method. The major sources ofpossible error are as follows:

(a) New rubber-balloon volumeters should becalibrated against several known volumes of differentsizes covering the volume range of in-place measure-ments.

(b) For stiff soils such as clay, it is possible totrap air between the sides of the sample hole and bal-loon. This error can be minimized by placing lengths ofsmall-diameter string over the edge of the hole anddown the inside wall slightly beyond the bottom cen-ter.

(c) The application of the 2- to 3-pounds-per-square-inch pressure to extend the balloon into exist-ing irregularities in the hole will cause a noticeable up-ward force on the volumeter. Care must be taken to en-sure that the volumeter remains in intimate contactwith the base plate.

(d) The rubber balloon must be frequentlychecked for leaks.

(3) Nuclear moisture-density method. The majorsources of possible error are as follows:

(a) The single consistent source of error is re-lated to the accuracy of the system. The overall systemaccuracy in determining densities is statistical in na-ture and appears to vary with the equipment used, testconditions, materials tested, and operators. If properprocedures are followed, the standard deviations interms of accuracy will vary on the order of 3 to 5pounds per cubic foot for density tests and 0.5 to 1.0pound of water per cubic foot of material for watercontent tests.

(b) Manufacturers furnish calibration curves foreach piece of equipment. Due to the effects of differingchemical compositions, calibration curves may not beapplicable to materials not represented in establishingthe calibration curve. Apparent variations in calibra-

whereT = time in the microwave oven, secondsMW

= mass of water present in the soil-watermixture, grams

w = water content of the specimen= initial temperature of the soil-water mass,

degree CentigradeP = power output of the oven, watts

This governing equation indicates that in order to pre-dict accurately the drying times required, an estimateof the specimen water content must be made and theoven power versus load relationship must be estab-lished by calibration.

(2) The limitation of having to estimate the initialwater content of the specimen is not insurmountable.Test results indicate that slight overestimations of theactual water content, i.e., longer drying times, general-ly result in small differences between conventionaloven and microwave oven water contents. Conversely,underestimations of water content result in more seri-ous errors. If an accurate estimate of water content

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TM 5-818-4/AFM 88-5, Chap. 5

cannot be made, experience has shown that close. vis-ual observation often can be used to determine if soiloverheating is occurring. An alternative approach is toincrementally dry a duplicate specimen until a con-stant weight is obtained, calculate the water content,and input this value into equation (B-1).

(3) The useful power output “P” is determined inthe laboratory by subjecting a mass of distilled waterto microwaves for a given time and then measuringthe rise in temperature induced in the water. Power inwatts is calculated from

where

t =

(B-2)

mass of distilled water in the oven, gramsincrease in temperature of the distilledwater, degree Centigradetime in the oven for calibration, seconds

A plot is then made of power output and oven load(mass of water in oven) in grams of water as shown infigure B-8.

Figure B-8. Power Applied by the Oven to Dry Moist Soils.

(4) The water content estimate is used to calculatethe mass of water in the specimen from

(B-3)

where= mass of the water in the specimen, and

equivalent to oven load in figure B-8,grams

= wet weight of the specimen, gramsBy calculating (oven load in fig. B-8) from

equation (B-1).(5) It may not be possible to successfully dry cer-

tain soils in the microwave oven. Gypsum may decom-pose and dehydrate under microwave excitation. High-ly metallic soils (iron ore, aluminum rich soils, andbauxite) have a high affinity for microwave energy andoverheat rapidly after all the free water has been va-porized. Hence, extreme care is required when dryingthese soils. For the same reason, metallic tare cans oraluminum plates are not permissible as specimen con-tainers.

(6) Because microwaves are a type of radiation,normal safety precautions to avoid undue exposureshould be observed.

b. Proctor penetrometer. The Proctor penetrationresistance method in the hands of inspection personnelexperienced in its use provides a rapid expedient checkon whether the field water content is adequate forproper compaction. However, the method is suitableonly for fine-grained soils because coarse sand or grav-el may cause erroneously high resistance readings. Themethod consists of compacting by the procedure usedfor control of a representative sample of soil takenfrom the loose lift being placed. The compacted speci-men is weighed, and the wet unit weight is deter-mined. The penetration resistance of the compactedspecimen in the mold is then measured with the soilpenetrometer. The moisture content can then be esti-mated by comparing the penetration resistance of fieldcompacted specimens with a relation previously estab-lished in the laboratory between wet unit weight,penetration resistance, and moisture content. The pro-cedure requires about 10 minutes and is sufficientlyaccurate for most field purposes. The procedure to de-termine the relation between wet unit weight, penetra-tion resistance, and moisture content is described inASTM D 1558. The relation is generally developed inconjunction with the compaction test.

equation (B-3) and finding a comparable value of pow-er from a plot similar to figure B-8 for the particularoven used, the drying time may be calculated from

c. Other methods. Other methods for determiningwater content include drying by hot plate or openflame, drying by forced hot air and a rapid moisturetest that uses calcium carbonate. In the hot platemethod, a small tin pan and a hot plate, oil burner, orgas burner (something to furnish fast heat) are used. Asample of wet soil is weighed, dried by one of the abovementioned methods, and weighed again to determinehow much water was in the sample. This method isfast, but care must be taken to ensure that the materi-al is thoroughly dry. Also, if both organic matter andbound water are removed, higher water content deter-minations than those obtained by ovendrying some-times result. In the forced hot air, a sample is placed in

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TM 5-818-4/AFM 88-5, Chap. 5

a commercially available apparatus containing an elec- weights from 25 to 500 grams. Drying times are esti-tric heater and blower. Hot air at 150 to 300 degrees mated to vary from 5 minutes for sand to as long as 30Fahrenheit is blown over and around the sample for a minutes for fat clay. The rapid moisture test and limi-preset time. A 110- or 230-volt source is required. tations are described in STP 479.Available sizes of apparatus can accommodate sample

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TM 5-818-4/AFM 88-5, Chap. 5

APPENDIX C

BIBLIOGRAPHY

Broms, B., “Lateral Earth Pressures Due to Compaction of Cohesionless Soils”. Proceedings, Fourth BudapestConference on Soil Mechanics and Foundation Engineering, Budapest, Hungary (1971).

Burmister, D. M., “The Grading-Density Relations of Granular Materials”. Proceedings, American Society forTesting and Materials, Volume 38, Part II, Philadelphia, Pennsylvania (1938).

Davis, F. J., “Quality Control of Earth Embankments”. International Conference on Soil Mechanics and Founda-tion Engineering, Volume 1, Switzerland (1953).

de Mello, U. F. B., Sonto Silveira, E. B., and Silveira, A., “True Representation of the Quality of a Compacted Em-bankment”. First Pan-American Conference on Soil Mechanics and Foundations Engineering, Volume II, Mexico(1960).

Hilf, J. W., “Compacting Earth Dams with Heavy Tamping Rollers”. Journal of the Soil Mechanics and Founda-tions Division, American Society of Civil Engineers, Volume 83, No. SM2, Paper 1205, Ann Arbor, Michigan(1957).

Ingold, T. S., “The Effects of Compaction on Retaining Walls”. Geotechnique, Volume 29, No. 3. London (1979).

Ingold, T. S., “Retaining Wall Performance During Backfilling”. Journal of the Geotechnical Engineering Division,American Society of Civil Engineers, Volume 105, GT5, Paper 14580, New York, New York (1979).

Li, C. Y., “Basic Concepts on the Compaction of Soil”. Journal of the Soil Mechanics and Foundations Division,American Society of Civil Engineers, Volume 82, SM1, Paper 862, Ann Arbor, Michigan (1956).

Joshi, R. C., Duncan, D. M. and Durbin, W. L., “Performance Record of Fly Ash as a Construction Material”. Pro-ceedings, Fourth International Ash Utilization Symposium, St. Louis, Missouri, 24-25 March 1976. John H. Faber,editor, Energy Research and Development Administration Morgantown, West Virginia (1976)(NTIS: MERC/SP-76/4).

Olson, R. E. “Effective Stress Theory of Soil Compaction”. Journal of the Soil Mechanics and Foundations Division,American Society of Civil Engineers, Volume 89, No. SM2, Paper 3457, Ann Arbor, Michigan (1963).

Plantema, G., “Influence of Density on Sounding Results in Dry, Moist, and Saturated Sands”. Proceedings of theFourth International Conference on Soil Mechanics and Foundation Engineering, Long Volume I (1957).

Proctor, R. S., “The Design and Construction of Rolled Earth Dams”. Engineering News-Record, Volume III (1933).

Quigley, D. W. and Duncan, J. M., “Earth Pressures on Conduits and Retaining Walls”. Report No. UCB/GT/78-06,University of California, Department of Civil Engineering (1978).

Turnbull, W. J. and Foster, C. R., “Stabilization of Materials by Compaction”. Journal of Soil Mechanics andFoundations Division, American Society of Civil Engineers, Volume 82, No. SM2, Paper 934, Ann Arbor, Michigan(1956).

Winterkorn, H. F. and Fang, Hsai-Yang, Foundation Engineering Handbook. Van Nostrand Reinhold Company,New York, New York (1975).

C-1

By Order of the Secretaries of the Army and the Air Force:

TM 5-818-4/AFM 88-5, Chap. 5

The proponent agency of this publication is the Office of the Chiefof Engineers, United States Army.Users are invited to send comments and suggested improvementson DA Form 2028 (Recommended Changes to Publications and BlankForms) direct to HQDA (DAEN-ECE-G), WASH DC 20314.

Official:ROBERT M. JOYCE

Major General, United States ArmyThe Adjutant General

E. C. MEYERGeneral, United States Army

Chief of Staff

Official:JAMES L. WYATT, JR., Colonel, USAFDirector of Administration

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DISTRIBUTION:Army: To be distributed in accordance with DA Form 12-34B, TM 5-800 Series requirements for Engineering

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*U.S. GOVERNMENT PRINTING OFFICE: 1983-605-040:190