CHAPTER 9 Soil Stabilization for Roads and Airfields · FM 5-410 CHAPTER 9 Soil Stabilization for Roads and Airfields Soil stabilization is the alteration of one or more soil properties,

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CHAPTER 9

S o i l S t a b i l i z a t i o n

f o r R o a d s a n d A i r f i e l d s

Soil stabilization is the alteration of one ormore soil properties, by mechanical or chemi-cal means, to create an improved soil materialpossessing the desired engineering proper-ties. Soils may be stabilized to increasestrength and durability or to prevent erosionand dust generation. Regardless of the pur-pose for stabilization, the desired result is thecreation of a soil material or soil system thatwill remain in place under the design use con-ditions for the design life of the project.

Engineers are responsible for selecting orspecifying the correct stabilizing method,technique, and quantity of material required.This chapter is aimed at helping to make thecorrect decisions. Many of the proceduresoutlined are not precise, but they will “get youin the ball park.” Soils vary throughout theworld, and the engineering properties of soilsare equally variable. The key to success insoil stabilization is soil testing. The methodof soil stabilization selected should be verifiedin the laboratory before construction andpreferably before specifying or orderingmaterials.

Section I. Methods ofStabilization

BASIC CONSIDERATIONSDeciding to stabilize existing soil material

in the theater of operations requires an as-sessment of the mission, enemy, terrain,

troops (and equipment), and time available(METT-T).

Mission. What type of facility is to beconstructed—road, airfield, or build-ing foundation? How long will thefacility be used (design life)?Enemy. Is the enemy interdictinglines of communications? If so, howwill it impact on your ability to haulstabilizing admixtures delivered toyour construction site?Terrain, Assess the effect of terrainon the project during the constructionphase and over the design life of thefacility. Is soil erosion likely? If so,what impact will it have? Is there aslope that is likely to become unstable?Troops (and equipment). Do you haveor can you get equipment needed toperform the stabilization operation?Time available. Does the tactical situa-tion permit the time required to stabi-lize the soil and allow the stabilizedsoil to cure (if necessary)?

There are numerous methods by whichsoils can be stabilized; however, all methodsfall into two broad categories. They are—

Mechanical stabilization.Chemical admixture stabilization.

Some stabilization techniques use a com-bination of these two methods. Mechanical

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stabilization relies on physical processes tostabilize the soil, either altering the physicalcomposition of the soil (soil blending) or plac-ing a barrier in or on the soil to obtain thedesired effect (such as establishing a sodcover to prevent dust generation). Chemicalstabilization relies on the use of an admixtureto alter the chemical properties of the soil toachieve the desired effect (such as using limeto reduce a soil’s plasticity).

Classify the soil material using the USCS.When a soil testing kit is unavailable, classifythe soil using the field identificationmethodology. Mechanical stabilizationthrough soil blending is the most economicaland expedient method of altering the existingmaterial. When soil blending is not feasibleor does not produce a satisfactory soilmaterial, geotextiles or chemical admixturestabilization should be considered. If chemi-cal admixture stabilization is beingconsidered, determine what chemical admix-tures are available for use and any specialequipment or training required to successfullyincorporate the admixture.

MECHANICAL STABILILIZATIONMechanical stabilization produces by com-

paction an interlocking of soil-aggregateparticles. The grading of the soil-aggregatemixture must be such that a dense mass isproduced when it is compacted. Mechanicalstabilization can be accomplished byuniformly mixing the material and then com-pacting the mixture. As an alternative,additional fines or aggregates maybe blendedbefore compaction to form a uniform, well-graded, dense soil-aggregate mixture aftercompaction. The choice of methods should bebased on the gradation of the material. Insome instances, geotextiles can be used to im-prove a soil’s engineering characteristics (seeChapter 11).

The three essentials for obtaining aproperly stabilized soil mixture are—

Proper gradation.A satisfactory binder soil.Proper control of the mixture content.

To obtain uniform bearing capacity, uniformmixture and blending of all materials is es-sential. The mixture will normally becompacted at or near OMC to obtain satisfac-tory densities.

The primary function of the portion of amechanically stabilized soil mixture that isretained on a Number 200 sieve is to con-tribute internal friction. Practically allmaterials of a granular nature that do not sof-ten when wet or pulverize under traffic can beused; however, the best aggregates are thosethat are made up of hard, durable, angularparticles. The gradation of this portion of themixture is important, as the most suitable ag-gregates generally are well-graded fromcoarse to fine. Well-graded mixtures arepreferred because of their greater stabilitywhen compacted and because they can becompacted more easily. They also havegreater increases in stability with cor-responding increases in density. Satisfactorymaterials for this use include—

Crushed stone.Crushed and uncrushed gravel.Sand.Crushed slag.

Many other locally available materialshave been successfully used, including disin-tegrated granite, talus rock, mine tailings,caliche, coral, limerock, tuff, shell, slinkers,cinders, and iron ore. When local materialsare used, proper gradation requirements can-not always be met.

NOTE: If conditions are encountered inwhich the gradation obtained by blend-ing local materials is either finer orcoarser than the specified gradation, thesize requirements of the finer fractionsshould be satisfied and the gradation ofthe coarser sizes should be neglected.

The portion of the soil that passes a Num-ber 200 sieve functions as filler for the rest ofthe mixture and supplies cohesion. This aidsin the retention of stability during dryweather. The swelling of clay material servessomewhat to retard the penetration of


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moisture during wet weather. Clay or dustfrom rock-crushing operations are commonlyused as binders. The nature and amount ofthis finer material must be carefully con-trolled, since too much of it results in an unac-ceptable change in volume with change inmoisture content and other undesirableproperties. The properties of the soil binderare usually controlled by controlling the plas-ticity characteristics, as evidenced by the LLand PI. These tests are performed on the por-tion of the material that passes a Number 40sieve. The amount of fines is controlled bylimiting the amount of material that maypass a Number 200 sieve. When the stabi-lized soil is to be subjected to frost action, thisfactor must be kept in mind when designingthe soil mixture.

UsesMechanical soil stabilization may be used

in preparing soils to function as—Subgrades.Bases.Surfaces.

Several commonly encountered situationsmay be visualized to indicate the usefulnessof this method. One of these situations occurswhen the surface soil is a loose sand that is in-capable of providing support for wheeledvehicles, particularly in dry weather. Ifsuitable binder soil is available in the area, itmay be brought in and mixed in the properproportions with the existing sand to providean expedient all-weather surface for lighttraffic. This would be a sand-clay road. Thisalso may be done in some cases to provide a“working platform” during constructionoperations. A somewhat similar situationmay occur in areas where natural gravelssuitable for the production of a well-gradedsand-aggregate material are not readilyavailable. Crushed stone, slag, or othermaterials may then be stabilized by the addi-tion of suitable clay binder to produce asatisfactory base or surface. A commonmethod of mechanically stabilizing an exist-ing clay soil is to add gravel, sand, or other

granular materials. The objectives here areto—

Increase the drainability of the soil.Increase stability.Reduce volume changes.Control the undeirable effects associatedwith clays.

ObjectiveThe objective of mechanical stabilization is

to blend available soils so that, when properlycompacted, they give the desired stability. Incertain areas, for example, the natural soil ata selected location may have low load-bearingstrength because of an excess of clay, silt, orfine sand. Within a reasonable distance,suitable granular materials may occur thatmay be blended with the existing soils tomarkedly improve the soil at a much lowercost in manpower and materials than is in-volved in applying imported surfacing.

The mechanical stabilization of soils inmilitary construction is very important. Theengineer needs to be aware of the possibilitiesof this type of construction and to understandthe principles of soil action previouslypresented. The engineer must fully inves-tigate the possibilities of using locallyavailable materials.

LimitationsWithout minimizing the importance of

mechanical stabilization, the limitations ofthis method should also be realized. Theprinciples of mechanical stabilization havefrequently been misused, particularly inareas where frost action is a factor in thedesign. For example, clay has been added to“stabilize” soils, when in reality all that wasneeded was adequate compaction to provide astrong, easily drained base that would not besusceptible to detrimental frost action. Anunderstanding of the densification that canbe achieved by modern compaction equip-ment should prevent a mistake of this sort.Somewhat similarly, poor trafficability of asoil during construction because of lack offines should not necessarily provide an excuse


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for mixing in clay binder. The problem maypossibly be solved by applying a thin surfacetreatment or using some other expedientmethod.

Soil Base RequirementsGrading requirements relative to mechani-

cally stabilized soil mixtures that serveas base courses are given in Table 7-3 ofTM 5-330 /Air Force Manual (AFM) 86-3,Volume II. Experience in civil highway con-struction indicates that best results areobtained with this type of mixture if the frac-tion passing the Number 200 sieve is notgreater than two-thirds of the fraction pass-ing the Number 40 sieve. The size of thelargest particles should not exceed two-thirdsof the thickness of the layer in which they areincorporated. The mixture should be well-graded from coarse to fine.

A basic requirement of soil mixtures thatare to be used as base courses is that the PIshould not exceed 5. Under certain cir-cumstances, this requirement may be relaxedif a satisfactory bearing ratio is developed,Experience also indicates that under idealcircumstances the LL should not exceed 25.These requirements may be relaxed intheater-of-operations construction. The re-quirements may be lowered to a LL of 35 anda PI of 10 for fully operational airfields. Foremergency and minimally operational air-fields, the requirements may be lowered to aLL of 45 and a PI of 15, when drainage is good.

Soil Surface RequirementsGrading requirements for mechanically

stabilized soils that are to be used directly assurfaces, usually under emergency condi-tions, are generally the same as those indi-cated in Table 7-3 of TM 5-330/AFM 86-3,Volume II. Preference should be given to mix-tures that have a minimum aggregate sizeequal to 1 inch or perhaps 1 ½ inches. Ex-perience indicates that particles larger thanthis tend to work themselves to the surfaceover a period of time under traffic. Somewhatmore fine soil is desirable in a mixture that isto serve as a surface, as compared with one fora base. This allows the surface to be moreresistant to the abrasive effects of traffic and

penetration of precipitation. To some extent,moisture lost by evaporation can be replacedby capillarity.

Emergency airfields that have surfaces ofthis type require a mixture with a PI between5 and 10. Experience indicates that road sur-faces of this type should be between 4 and 9.The surface should be made as tight as pos-sible, and good surface drainage should beprovided. For best results, the PI of a stabi-lized soil that is to function first as a wearingsurface and then as a base, with a bituminoussurface being provided at a later date, shouldbe held within very narrow limits. Con-sideration relative to compaction, bearingvalue, and frost action are as important forsurfaces of this type as for bases.

ProportioningMixtures of this type are difficult to design

and build satisfactorily without laboratorycontrol. A rough estimate of the properproportions of available soils in the field ispossible and depends on manual and visualinspection. For example, suppose that a loosesand is the existing subgrade soil and it isdesired to add silty clay from a nearby borrowsource to achieve a stabilized mixture. Eachsoil should be moistened to the point where itis moist, but not wet; in a wet soil, the mois-ture can be seen as a shiny film on the surface,What is desired is a mixture that feels grittyand in which the sand grains can be seen.Also, when the soils are combined in theproper proportion, a cast formed by squeezingthe moist soil mixture in the hand will not beeither too strong or too weak; it should just beable to withstand normal handling withoutbreaking. Several trial mixtures should bemade until this consistency is obtained. Theproportion of each of the two soils should becarefully noted. If gravel is available, thismay be added, although there is no real rule ofthumb to tell how much should be added. It isbetter to have too much gravel than too little.

Use of Local Materials. The essence ofmechanical soil stabilization is the use of lo-cally available materials. Desirable require-ments for bases and surfaces of this type weregiven previously. It is possible, especiallyunder emergency conditions, that mixtures of


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local materials will give satisfactory service,even though they do not meet the stated re-quirements. Many stabilized mixtures havebeen made using shell, coral, soft limestone,cinders, marl, and other materials listed ear-lier. Reliance must be placed on—

Experience.An understanding of soil action.The qualities that are desired in thefinished product.Other factors of local importance inproportioning such mixtures in thefield.

Blending. It is assumed in this discussionthat an existing subgrade soil is to be stabi-lized by adding a suitable borrow soil toproduce a base course mixture that meets thespecified requirements. The mechanicalanalysis and limits of the existing soil willusually be available for the results of the sub-grade soil survey (see Chapter 3). Similarinformation is necessary concerning the bor-row soil. The problem is to determine theproportions of these two materials thatshould be used to produce a satisfactory mix-ture. In some cases, more than two soils mustbe blended to produce a suitable mixture.However, this situation is to be avoided whenpossible because of the difficulties frequentlyencountered in getting a uniform blend ofmore than two local materials. Trial com-binations are usually made on the basis of themechanical analysis of the soil concerned. Inother words, calculations are made to deter-mine the gradation of the combined materialsand the proportion of each component ad-justed so that the gradation of thecombination falls within specified limits. ThePI of the selected combination is then deter-mined and compared with the specification.If this value is satisfactory, then the blendmay be assumed to be satisfactory, providedthat the desired bearing value is attained. Ifthe plasticity characteristics of the first comb-ination are not within the specified limits,additional trials must be made. The propor-tions finally selected then may be used in thefield construction process.

Numerical Proportioning. The process ofproportioning will now be illustrated by a

numerical example (see Table 9-1, page 9-6).Two materials are available, material B in theroadbed and material A from a nearby borrowsource. The mechanical analysis of each ofthese materials is given, together with the LLand PI of each. The desired grading of thecombination is also shown, together with thedesired plasticity characteristics.

Specified Gradation. Proportioning oftrial combinations may be done arithmetical-ly or graphically. The first step in usingeither the graphical or arithmetical method isto determine the gradation requirements.Gradation requirements for base course, sub-course, and select material are found inTables 7-1 and 7-3, TM 5-330/AFM 86-3,Volume II. In the examples in Figures 9-1and 9-2, page 9-7, abase course material witha maximum aggregate size of 1 inch has beenspecified. In the graphical method, thegradation requirements are plotted to theoutside of the right axis. In the arithmeticalmethod, they are plotted in the columnlabelled “Specs.” Then the gradations of thesoils to be blended are recorded. The graphi-cal method has the limitation of only beingcapable of blending two soils, whereas thearithmetical method can be expanded toblend as many soils as required. At this point,the proportioning methods are distinctiveenough to require separate discussion.

Graphical Proportioning. The actualgradations of soil materials A and B areplotted along the left and right axes of thegraph, respectively. As shown in Figure 9-1,page 9-7, material A has 92 percent passingthe 3/4-inch sieve while material B has 72percent passing the same sieve. Once plotted,a line is drawn across the graph, connectingthe percent passing of material A with thepercent passing of material B for each sievesize.

NOTE: Since both materials A and B had100 percent passing the l-inch sieve, itwas omitted from the graph and willnot affect the results.

Mark the point where the upper and lowerlimits of the gradation requirements intersect


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the line for each sieve size. In Figure 9-1, theallowable percent passing the Number 4 sieveranges from 35 to 65 percent passing. Thepoint along the Number 4 line at which 65percent passing intersects represents 82 per-cent material A and 18 percent material B.The 35 percent passing intersects the Num-ber 4 line at 19 percent material A and 81percent material B. The acceptable ranges ofmaterial A to be blended with material B isthe widest range that meets the gradation re-quirements for all sieve sizes. The shadedarea of the chart represents the combinationsof the two materials that will meet thespecified gradation requirements. Theboundary on the left represents the combina-tion of 44 percent material A and 56 percentmaterial B. The position of this line is fixedby the upper limit of the requirement relatingto the material passing the Number 200 sieve(15 percent). The boundary on the right rep-resents the combination of 21 percentmaterial A and 79 percent material B. Thisline is established by the lower limit of the re-quirement relative to the fraction passing theNumber 40 sieve (15 percent). Any mixturefalling within these limits satisfies the grada-tion requirements. For purposes ofillustration, assume that a combination of 30percent material A and 70 percent material

B is selected for a trial mixture, A similardiagram can be prepared for any two soils.

Arithmetical Proportioning. Record theactual gradation of soils A and B in theirrespective columns (Columns 1 and 2, Figure9-2). Average the gradation limits and recordin the column labelled "S". For example, theallowable range for percent passing a 3/8-inchsieve in a 1-inch minus base course is 50 to 80percent. The average, 50±80/2, is 65 percent.As shown in Figure 9-2, S for 3/8 inch is 65.Next, determine the absolute value of S-Aand S-B for each sieve size and record in thecolumns labelled “ (S-A)“ and “ (S-B), res-pectively. Sum columns (S-A) and ( S-B).To determine the percent of soil A in the finalmix, use the formula—

In the example in Figure 9-2:

103 103134 + 103 x 100% = 43.5%= 2 3 7

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The percent of soil B in the final mix can bedetermined by the formula:

or

100% - %A = %B

NOTE: If three or more soils are to beblended, the formula would be—

%C =

This formula can be further expanded asnecessary.

Multiply the percent passing each sieve forsoil A by the percentage of soil A in the finalmix; record the information in column 4 (seeFigure 9-2, page 9-7), Repeat the procedurefor soil B and record the information incolumn 5 (see Figure 9-2, page 9- 7). Completethe arithmetical procedure by addingcolumns 4 and 5 to obtain the percent passingeach sieve in the blended soil.

Both the graphical and arithmeticalmethods have advantages and disad-vantages. The graphical method eliminatesthe need for precise blending under field con-ditions and the methodology requires lesseffort to use, Its drawback becomes very com-plex when blending more than two soils. Thearithmetical method allows for more preciseblending, such as mixing at a batch plant, andit can be readily expanded to accommodatethe blending of three or more soils. It has thedrawback in that precise blending is often un-attainable under field conditions. Thisreduces the quality assurance of the perfor-mance of the blended soil material.

Plasticity Requirements. A method ofdetermining the PI and LL of the combinedsoils serves as a method to indicate if theproposed trial mixture is satisfactory, pend-ing the performance of laboratory tests. Thismay be done either arithmetically or graphi-cally. A graphical method of obtaining these


approximate values is shown in Figure 9-3.The values shown in Figure 9-3 require addi-tional explanation, as follows. Consider 500pounds of the mixture tentatively selected (30percent as material A and 70 percent asmaterial B). Of this 500 pounds, 150 poundsare material A and 350 pounds material B.Within the 150 pounds of material A, thereare 150 (0.52) = 78 pounds of material passingthe Number 40 sieve. Within the 350 poundsof material B, there are 150 (0.05) = 17.5pounds of material passing the Number 40sieve. The total amount of material passingthe Number 40 sieve in the 500 pounds ofblend = 78+ 17.5= 95.5 pounds, The percent-age of this material that has a PI of 9(material A) is (78/95.5) 100= 82. As shown inFigure 9-3, the approximate PI of the mixtureof 30 percent material A and 70 percentmaterial B is 7.4 percent. By similar reason-ing, the approximate LL of the blend is 28,4percent. These values are somewhat higherthan permissible under the specification. Anincrease in the amount of material B willsomewhat reduce the PI and LL of the com-bination.

Field Proportioning. In the field, thematerials used in a mechanically stabilizedsoil mixture probably will be proportioned byloose volume. Assume that a mixture incor-porates 75 percent of the existing subgradesoil, while 25 percent will be brought in froma nearby borrow source. The goal is to con-struct a layer that has a compacted thicknessof 6 inches. It is estimated that a loose thick-ness of 8 inches will be required to form the6-inch compacted layer. A more exactrelationship can be established in the field asconstruction proceeds, Of the 8 inches loosethickness, 75 percent (or 0.75(8) = 6 inches)will be the existing soil, The remainder of themix will be mixed thoroughly to a depth of8 inches and compacted by rolling. Theproportions may be more accurately control-led by weight, if weight measurements can bemade under existing conditions.

WaterproofingThe ability of an airfield or road to sustain

operations depends on the bearing strength ofthe soil. Although an unsurfaced facility maypossess the required strength when initiallyconstructed, exposure to water can result i n a

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loss of strength due to the detrimental effectof traffic operations. Fine-grained soils orgranular materials that contain an excessiveamount of fines generally are more sensitiveto water changes than coarse-grained soils.Surface water also may contribute to thedevelopment of dust by eroding or looseningmaterial from the ground surface that can be-come dust during dry weather conditions.

Sources of Water. Water may enter a soileither by the percolation of precipitation orponded surface water, by capillary action ofunderlying ground water, by a rise in thewater-table level, or by condensation of watervapor and accumulation of moisture under avapor-impermeable surface. As a generalrule, an existing groundwater table at shal-low depths creates a low load-bearingstrength and must be avoided wherever pos-sible. Methods to protect against moistureingress from sources other than the groundsurface will not be considered here. In mostinstances, the problem of surface water can belessened considerably by following the properprocedures for—

Grading.

Compaction.Drainage.

Objectives of Waterproofers. The objec-tive of a soil-surface waterproofer is to protecta soil against attack by water and thuspreserve its in-place or as-constructedstrength during wet-weather operations.The use of soil waterproofers generally islimited to traffic areas. In some instances,soil waterproofers may be used to prevent ex-cessive softening of areas, such as shouldersor overruns, normally considered nontrafficor limited traffic areas.

Also, soil waterproofers may prevent soilerosion resulting from surface water runoff.As in the case of dust palliative, a thin orshallow-depth soil waterproofing treatmentloses its effectiveness when damaged by ex-cessive rutting and thus can be usedefficiently only in areas that are initially firm.Many soil waterproofers also function well asdust palliatives; therefore, a single materialmight be considered as a treatment in areaswhere the climate results in both wet and drysoil surface conditions. Geotextiles are the


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primary means of waterproofing soils whengrading, compaction, and drainage practicesare insufficient. Use of geotextiles is dis-cussed in detail in Chapter 11.

CHEMICAL ADMIXTURE STABILIZATIONChemical admixtures are often used to sta-

bilize soils when mechanical methods ofstabilization are inadequate and replacing anundesirable soil with a desirable soil is notpossible or is too costly. Over 90 percent of allchemical admixture stabilization projectsuse—

Cement.Lime.Fly ash.Bituminous materials.

Other stabilizing chemical admixtures areavailable, but they are not discussed in thismanual because they are unlikely to be avail-able in the theater of operations.

WARNINGChemical admixtures may contain haz-ardous materials, Consult Appendix Cto determine the necessary safetyprecautions for the selected admixture.

When selecting a stabilizer additive, thefactors that must be considered are the—

Type of soil to be stabilized.Purpose for which the stabilized layerwill be used.Type of soil quality improvementdesired.Required strength and durability ofthe stabilized layer.Cost and environmental conditions.

Table 9-2 lists stabilization methods mostsuitable for specific applications. To deter-mine the stabilizing agent(s) most suited to aparticular soil, use the gradation triangle inFigure 9-4, page 9-12, to find the area that cor-responds to the gravel, sand, and fine contentof the soil. For example, soil D has the follow-ing characteristics:

With 95 percent passing the Numbersieve, the PI is 14.With 14 percent passing the Number200 sieve, the LL is 21.

Therefore the soil is 5 percent gravel, 81percent sand, and 14 percent fines. Figure9-4, page 9-12, shows this soil in Area 1C.

Table 9-3, page 9-13, shows that thestabilizing agents recommended for Area 1Csoils include bituminous material, portlandcement, lime, and lime-cement-fly ash. Inthis example, bituminous agents cannot beused because of the restriction on PI, but anyof the other agents can be used if available.

CementCement can be used as an effective stabi-

lizer for a wide range of materials. In general,however, the soil should have a PI less than30. For coarse-grained soils, the percentpassing the Number 4 sieve should be greaterthan 45 percent.

If the soil temperature is less than 40degrees Fahrenheit and is not expected to in-crease for one month, chemical reactions willnot occur rapidly. The strength gain of the ce-ment-soil mixture will be minimal. If theseenvironmental conditions are anticipated,the cement may be expected to act as a soilmodifier, and another stabilizer might be con-sidered for use. Soil-cement mixtures shouldbe scheduled for construction so that suffi-cient durability will be gained to resist anyfreeze-thaw cycles expected.

Portland cement can be used either tomodify and improve the quality of the soil orto transform the soil into a cemented mass,which significantly increases its strength anddurability. The amount of cement additivedepends on whether the soil is to be modifiedor stabilized. The only limitation to theamount of cement to be used to stabilize ormodify a soil pertains to the treatment of thebase courses to be used in flexible pavementsystems. When a cement-treated base coursefor Air Force pavements is to be surfaced with


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asphaltic concrete, the percent of cement by find the design cement content based on totalweight is limited to 4 percent. sample weight expressed as—

Modification. The amount of cement re- A = 100Bcquired to improve the quality of the soilthrough modification is determined by the where—trial-and-error approach. To reduce the PI ofthe soil, successive samples of soil-cement A=mixtures must be prepared at different treat-ment levels and the PI of each mixturedetermined. B=

The minimum cement content that yieldsthe desired PI is selected, but since it was c =determined based on the minus 40 fraction ofthe material, this value must be adjusted to

design cement content, percent oftotal weight of soil

percent passing Number 40 sieve, expressed as a decimal

percent of cement required to obtainthe desired PI of minus Number 40material, expressed as a decimal


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If the objective of modification is to im-prove the gradation of granular soil throughthe addition of fines, the analysis should beconducted on samples at various treatmentlevels to determine the minimum acceptablecement content. To determine the cementcontent to reduce the swell potential of fine-grained plastic soils, mold several samples atvarious cement contents and soak thespecimens along with untreated specimensfor four days. The lowest cement content thateliminates the swell potential or reducesthe swell characteristics to the minimum

becomes the design cement content. The ce-ment content determined to accomplish soilmodification should be checked to see if itprovides an unconfined compressive strengthgreat enough to qualify for a reduced thick-ness design according to criteria establishedfor soil stabilization (see Tables 9-4 and 9-5,page 9-14).

Cement-modified soil may be used in frostareas also. In addition to the procedures forthe mixture design described above, curedspecimens should be subjected to the 12


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freeze-thaw cycles test (omit wire brush por-tion) or other applicable freeze-thaw pro-cedures. This should be followed by a frost-susceptibility test, determined after freeze-thaw cycling, and should meet the require-ments set forth for the base course. If cement-modified soil is used as the subgrade, its frostsusceptibility (determined after freeze-thawcycling) should be used as the basis of thepavement thickness design if the reducedsubgrade-strength design method is applied.

Stabilization. The following procedure isrecommended for determining the design ce-ment content for cement-stabilized soils:

Step 1. Determine the classificationand gradation of the untreated soil.The soil must meet the gradation re-quirements shown in Table 9-6 beforeit can be used in a reduced thicknessdesign (multilayer design).

Step 2. Select an estimated cementcontent from Table 9-7 using the soilclassification.

Step 3. Using the estimated cementcontent, determine the compactioncurve of the soil-cement mixture.

Step 4. If the estimated cement con-tent from step 2 varies by more than±2 percent from the value in Tables9-8 or 9-9, page 9-16, conductadditional compaction tests, varyingthe cement content, until the valuefrom Table 9-8 or 9-9, page 9-16, iswithin 2 percent of that used for themoisture-density test.

NOTE: Figure 9-5, page 9-17, is used inconjunction with Table 9-9, page 9-16.The group index is obtained from Fig-ure 9-5, page 9-17 and used to enterTable 9-9, page 9-16.

Step 5. Prepare samples of the soil-cement mixture for unconfined com-pression and durability tests at the drydensity and at the cement contentdetermined in step 4. Also preparesamples at cement contents 2 percentabove and 2 percent below thatdetermined in step 4. The samplesshould be prepared according toTM 5-530 except that when morethan 35 percent of the material isretained on the Number 4 sieve,


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a CBR mold should be used toprepare the specimens. Cure thespecimens for seven days in a humidroom before testing. Test three spec-imens using the unconfined com-pression test and subject three spec-imens to durability tests. These testsshould be either wet-dry tests forpavements located in nonfrost areasor freeze-thaw tests for pavementslocated in frost areas.

Step 6. Compare the results of theunconfined compressive strength anddurability tests with the require-ments shown in Tables 9-4 and 9-5.

The lowest cement content thatmeets the required unconfined com-pressive strength requirementand demonstrates the requireddurability is the design content.If the mixture should meet thedurability requirements but notthe strength requirements, themixture is considered to be amodified soil.

Theater-of-operations construction re-quires that the engineer make maximum useof the locally available constructionmaterials. However, locally availablematerials may not lend themselves to


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classification under the USCS method. Theaverage cement requirements of common lo-cally available construction materials isshown in Table 9-10.

LimeExperience has shown that lime reacts with

medium-, moderately fine-, and fine-grainedsoils to produce decreased plasticity, in-creased workability and strength, andreduced swell. Soils classified according tothe USCS as (CH), (CL), (MH), (ML), (SC),(SM), (GC), (GM), (SW-SC), (SP-SC), (SM-SC), (GW-GC), (GP-GC), and (GM-GC)should be considered as potentially capable ofbeing stabilized with lime.

If the soil temperature is less than 60degrees Fahrenheit and is not expected to in-crease for one month, chemical reactions willnot occur rapidly. Thus, the strength gain ofthe lime-soil mixture will be minimal. Ifthese environmental conditions are expected,the lime may be expected to act as a soilmodifier. A possible alternative stabilizermight be considered for use. Lime-soil mix-tures should be scheduled for construction sothat sufficient durability is gained to resistany freeze-thaw cycles expected.

If heavy vehicles are allowed on the lime-stabilized soil before a 10- to 14-day curingperiod, pavement damage can be expected.Lime gains strength slowly and requiresabout 14 days in hot weather and 28 days incool weather to gain significant strength. Un-surfaced lime-stabilized soils abrade rapidlyunder traffic, so bituminous surface treat-ment is recommended to prevent surfacedeterioration.

Lime can be used either to modify some ofthe physical properties and thereby improvethe quality of a soil or to transform the soilinto a stabilized mass, which increases itsstrength and durability. The amount of limeadditive depends on whether the soil is to re-modified or stabilized. The lime to be usedmay be either hydrated or quicklime, al-though most stabilization is done usinghydrated lime. The reason is that quicklimeis highly caustic and dangerous to use. Thedesign lime contents determined from thecriteria presented herein are for hydratedlime. As a guide, the lime contents deter-mined herein for hydrated lime should bereduced by 25 percent to determine a designcontent for quicklime.


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Modification. The amount of lime requiredto improve the quality of a soil is determinedthrough the same trial-and-error processused for cement-modified soils.

Stabilization. To take advantage of thethickness reduction criteria, the lime-stabi-lized soil must meet the unconfinedcompressive strengths and durability re-quirements shown in Tables 9-4 and 9-5, page9-14, respectively.

When lime is added to a soil, a com-bination of reactions begins to take placeimmediately. These reactions are nearly com-plete within one hour, althoughsubstantial strength gain is not reflectedfor some time. The reactions result in achange in both the chemical compositionand the physical properties. Most lime hasa pH of about 12.4 when placed in awater solution. Therefore, the pH is a goodindicator of the desirable lime content of asoil-lime mixture. The reaction that takesplace when lime is introduced to a soilgenerally causes a significant change in theplasticity of the soil, so the changes in thePL and the LL also become indicators ofthe desired lime content. Two methods fordetermination of the initial design limecontent are presented in the following steps:

Step 1. The preferred method is toprepare several mixtures at differentlime-treatment levels and determinethe pH of each mixture after onehour. The lowest lime content pro-ducing the highest pH of the soil-limemixtures is the initial design limecontent. Procedures for conducting apH test on lime-soil mixtures arepresented in TM 5-530. In frost areas,specimens must be subjected to thefreeze-thaw test as discussed in step 2below. An alternate method of deter-mining an initial design lime contentis shown in Figure 9-6, page 9-20.Specific values required to use thisfigure are the PI and the percent ofmaterial passing the Number 40 sieve.These properties are determined fromthe PL and the gradation test on the

untreated soil for expedient construc-tion; use the amount of stabilizer deter-mined from the pH test or Figure 9-6,page 9-20.

Step 2. After estimating the initiallime content, conduct a compactiontest with the lime-soil mixture. Thetest should follow the same pro-cedures for soil-cement except themixture should cure no less than onehour and no more than two hours in asealed container before molding.Compaction will be accomplished infive layers using 55 blows of a10-pound hammer having an 18-inchdrop (CF 55). The moisture densityshould be determined at lime con-tents equal to design plus 2 percentand design plus 4 percent for thepreferred method at design ± 2 per-cent for the alternate method, Infrost areas, cured specimens shouldbe subjected to the 12 freeze-thawcycles (omit wire brush portion) orother applicable freeze-thaw pro-cedures, followed by frost sus-ceptibility determinations in stan-dard laboratory freezing tests.For lime-stabilized or lime-modifiedsoil used in lower layers of the basecourse, the frost susceptibility (deter-mined after freeze-thaw cycling)should meet the requirements for thebase course. If lime-stabilized or lime-modified soil is used as the subgrade,its frost susceptibility (determinedafter freeze-thaw cycling) should bethe basis of the pavement thicknessdesign if the reduced subgrade strengthdesign method is applied.

Step 3. Uniformed compression testsshould be performed it the designpercent of maximum density on threespecimens for each lime contenttested. The design value would thenbe the minimum lime content yieldingthe required strength. Procedures forthe preparation of lime-soil specimensare similar to those used for cement-stabilized soils with two exceptions:


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I

Soil Stabilization for Roads and AirfieIds 9-20

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after mixing, the lime-soil mixtureshould be allowed to mellow for notless than one hour nor more than twohours; after compaction, each spec-imen should be wrapped securely toprevent moisture loss and should becured in a constant-temperature cham-ber at 73 degrees Fahrenheit ±2degrees Fahrenheit for 28 days. Pro-cedures for conducting unconfinedcompression tests are similar to thoseused for soil-cement specimens exceptthat in lieu of moist curing, the lime-soil specimens should remain securelywrapped until testing.

Step 4. Compare the results of theunconfined compressive tests with thecriteria in Table 9-4, page 9-14. Thedesign lime content must be the low-est lime content of specimens meetingthe strength criteria indicated.

Other Additives. Lime may be used as apreliminary additive to reduce the PI or altergradation of a soil before adding the primarystabilizing agent (such as bitumen or ce-ment). If this is the case, then the design limecontent is the minimum treatment level thatwill achieve the desired results. For nonplas-tic and low-PI materials in which lime alonegenerally is not satisfactory for stabilization,fly ash may be added to produce the necessaryreaction.

Fly AshFly ash is a pozzolanic material that con-

sists mainly of silicon and aluminumcompounds that, when mixed with lime andwater, forms a hardened cementitious masscapable of obtaining high compressionstrengths. Fly ash is a by-product of coal-fired, electric power-generation facilities.The liming quality of fly ash is highly depend-ent on the type of coal used in powergeneration. Fly ash is categorized into twobroad classes by its calcium oxide (CaO) con-tent. They are—

Class C.Class F.

Class C. This class of fly ash has a high CaOcontent (12 percent or more) and originatesfrom subbituminous and lignite (soft) coal.Fly ash from lignite has the highest CaO con-tent, often exceeding 30 percent. This typecan be used as a stand-alone stabilizingagent. The strength characteristics of ClassC fly ash having a CaO less than 25 percentcan be improved by adding lime. Further dis-cussion of fly ash properties and a listing ofgeographic locations where fly ash is likely tobe found are in Appendix B.

Class F. This class of fly ash has a low CaOcontent (less than 10 percent) and originatesfrom anthracite and bituminous coal. Class Ffly ash has an insufficient CaO content for thepozzolanic reaction to occur. It is not effectiveas a stabilizing agent by itself; however, whenmixed with either lime or lime and cement,the fly ash mixture becomes an effectivestabilizing agent.

Lime Fly Ash Mixtures. LF mixtures cancontain either Class C or Class F fly ash. TheLF design process is a four-part process thatrequires laboratory analysis to determine theoptimum fines content and lime-to-fly-ashratio.

Step 1. Determine the optimum finescontent. This is the percentage of flyash that results in the maximum den-sity of the soil mix. Do this by con-ducting a series of moisture-densitytests using different percentages offly ash and then determining the mixlevel that yields maximum density.The initial fly ash content should beabout 10 percent based on the weightof the total mix. Prepare test samplesat increasing increments (2 percent)of fly ash, up to 20 percent. Thedesign fines content should be 2 per-cent above the optimum fines content.For example, if 14 percent fly ashyields the maximum density, thedesign fines content would be 16 per-cent. The moisture density relationwould be based on the 16 percentmixture.


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Step 2. Determine the rates of lime tofly ash, Using the design fines con-tent and the OMC determined in step1, prepare triplicate test samples atLF ratios of 1:3, 1:4, and 1:5. Cure alltest samples in sealed containers forseven days at 100 degrees Fahrenh-eit .

Step3. Evaluate the test samples forunconfined compressive strength. Iffrost is a consideration, subject a setof test samples to 12 cycles of freeze-thaw durability tests (refer to FM5-530 for actual test procedures).

Step 4. Determine the design LFratio. Compare the results of theunconfined strength test andfreeze-thaw durability tests with theminimum requirements found inTables 9-4 and 9-5, page 9-14,respectively. The LF ratio with thelowest lime content that meets therequired unconfined compressivestrength and demonstrates therequired durability is the design LFcontent. The treated material must alsomeet frost susceptibility requirementsas indicated in Special Report 83-27. Ifthe mixture meets the durabilityrequirements but not the strengthrequirements, it is considered to be amodified soil. If neither strength nordurability criteria are met, a differentLF content may be selected and thetesting procedure repeated.

Lime-Cement-Fly Ash (LCF) Mixtures.The design methodology for determining theLCF ratio for deliberate construction is thesame as for LF except cement is added in step2 at the ratio of 1 to 2 percent of the designfines content. Cement may be used in place ofor in addition to lime; however, the designfines content should be maintained.

When expedient construction is required,use an initial mix proportion of 1 percentportland cement, 4 percent lime, 16 per-cent fly ash, and 79 percent soil. Minimum

unconfined strength requirements (seeTable 9-4, page 9-14) must be met. If testspecimens do not meet strength require-ments, add cement in 1/2 percent incrementsuntil strength is adequate. In frost-suscep-tible areas, durability requirements mustalso be satisfied (see Table 9-5, page 9-14).

As with cement-stabilized base coursematerials, LCF mixtures containing morethan 4 percent cement cannot be used as basecourse material under Air Force airfield pave-ments.

Bituminous MaterialsTypes of bituminous-stabilized soils are—

Soil bitumen. A cohesive soil systemmade water-resistant by admixture.Sand bitumen. A system in whichsand is cemented together by bitumi-nous material.Oiled earth. An earth-road systemmade resistant to water absorptionand abrasion by means of a sprayedapplication of slow- or medium-curingliquid asphalt.Bitumen-waterproofed, mechanicallystabilized soil. A system in which twoor more soil materials are blended toproduce a good gradation of particlesfrom coarse to fine. Comparativelysmall amounts of bitumen are needed,and the soil is compacted.Bitumen-lime blend. A system in whichsmall percentages of lime are blendedwith fine-grained soils to facilitate thepenetration and mixing of bitumensinto the soil.

Soil Gradation. The recommended soilgradations for subgrade materials and baseor subbase course materials are shown inTables 9-11 and 9-12, respectively. Mechani-cal stabilization may be required to bring soilto proper gradation.

Types of Bitumen. Bituminous stabiliza-tion is generally accomplished using—

Asphalt cement.Cutback asphalt.Asphalt emulsions.


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The type of bitumen to be used depends on- -the type of soil to be stabilized, the method ofconstruction, and the weather conditions. Infrost areas, the use of tar as a binder should beavoided because of its high-temperature sus-ceptibility. Asphalts are affected to a lesserextent by temperature changes, but a grade ofasphalt suitable to the prevailing climateshould be selected. Generally the most satis-factory results are obtained when the mostviscous liquid asphalt that can be readilymixed into the soil is used. For higher qualitymixes in which a central plant is used,viscosity-grade asphalt cements should beused. Much bituminous stabilization is per-formed in place with the bitumen beingapplied directly on the soil or soil-aggregatesystem. The mixing and compaction opera-tions are conducted immediately thereafter.For this type of construction, liquid asphalts(cutbacks and emulsions) are used. Emul-sions are preferred over cutbacks because ofenergy constraints and pollution control ef-fects. The specific type and grade of bitumendepends on the characteristics of the ag-gregate, the type of construction equipment,and the climatic conditions. Table 9-13, page9-24, lists the types of bituminous materialsfor use with soils having different gradations.

Mix Design. Guidance for the design ofbituminous-stabilized base and subbase cour-ses is contained in TM 5-822-8. For subgradestabilization, the following equation may beused for estimating the preliminary quantityof cutback asphalt to be selected:

P =

where—

P =

a =

b =

c=

d=

S=

percent of cutback asphalt by weightof dry aggregate

percent of mineral aggregate retainedon Number 50 sieve

percent of mineral aggregate passingNumber 50 and retained onNumber 100 sieve

percent of mineral aggregate passingNumber 100 and retained onNumber 200 sieve

percent of mineralNumber 200 sieve

percent solvent

aggregate passing

The preliminary quantity of emulsified as-phalt to be used in stabilizing subgrades canbe determined from Table 9-14, page 9-24.Either cationic or anionic emulsions can beused. To ascertain which type of emulsion is


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preferred, first determine the general type ofaggregate. If the aggregate contains a highcontent of silica, as shown in Figure 9-7, page9-25, a cationic emulsion should be used (seeFigure 9-8, page 9-25.). If the aggregate is acarbonate rock (limestone, for example), ananionic emulsion should be used.

Figures 9-9 and 9-10 can be used to find themix design for asphalt cement. Thesepreliminary quantities are used for expedientconstruction. The final design content of as-phalt should be selected based on the resultsof the Marshall stability test procedure. Theminimum Marshall stability recommendedfor subgrades is 500 pounds; for base courses,750 pounds is recommended. If a soil does notshow increased stability when reasonableamounts of bituminous materials are added,the gradation of the soil should be modified oranother type of bituminous material shouldbe used. Poorly graded materials may be

improved by adding suitable fines containingconsiderable material passing a Number 200sieve. The amount of bitumen required for agiven soil increases with an increase in per-centage of the finer sizes.

Section II. Design ConceptsSTRUCTURAL CATEGORIES

Procedures are presented for determiningdesign thicknesses for two structuralcategories of pavement. They are—

Single-layer.Multilayer.

Typical examples of these pavements are in-dicated in Figure 9-11.

A typical single-layer pavement is a stabi-lized soil structure on a natural subgrade.The stabilized layer may be mixed in place orpremixed and later placed over the existingsubgrade. A waterproofing surface such asmembrane or a single bituminous surface(SBST) or a double bituminous surface treat-ment (DBST) may also be provided. Amultilayer structure typically consists of atleast two layers, such as a base and a wearingcourse, or three layers, such as a subbase, abase, and a wearing course. A thinwaterproofing course may also be used onthese structures. Single-layer and multi-layer pavement design procedures arepresented for all categories of roads and forcertain categories of airfields as indicated inTable 9-15, page 9-28.


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Both single-layer and multilayer pavementstructures may be constructed under eitherthe expedient or nonexpedient concept. Dif-ferent structural designs are provided toallow the design engineer wider latitude ofchoice. However, single-layer structures areoften associated with expedient constructionrather than nonexpedient construction, andmulti layers are nonexpedient and per-manent. Certain considerations should bestudied to determine whether to use a single-layer or mulilayer design under eitherconcept.

The overall concept of design as describedherein can be defined in four basic determina-tions as indicated in Table 9-16.

STABILIZED PAVEMENTDESIGN PROCEDURE

To use different stabilized materials effec-tively in transportation facilities, the designprocedure must incorporate the advantagesof the higher quality materials. These ad-vantages are usually reflected in betterperformance of the structures and a reductionin total thicknesses required. From astandpoint of soil stabilization (not modifica-tion), recent comparisons of behavior basedon type and quality of material have shownthat stabilization provides definite structuralbenefits. Design results for airfield and road


classifications are presented to provideguidance to the designer in determiningthickness requirements when using stabi-lized soil elements. The design thickness alsoprovides the planner the option of comparingthe costs of available types of pavement con-struction, thereby providing the beststructure for the situation.

The design procedure primarily incorporatesthe soil stabilizers to allow a reduction ofthickness from the conventional flexiblepavement-design thicknesses. These thick-ness reductions depend on the properconsideration of the following variables:

Load.Tire pressure.Design life.Soil properties.Soil strength.Stabilizer type.Environmental conditions.Other factors.

The design curves for theater-of-operationsairfields and roads are given for single-layerand multi layer pavements later in this sec-tion.

In the final analysis, the choice of the ad-mixture to be used depends on the economics

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and availability of the materials involved.The first decision that should be made iswhether stabilization should be attemptedat all. In some cases, it may be economicalmerely to increase the compaction require-ments or, as a minimum, to resort toincreased pavement thickness. If locallyavailable borderline or unacceptablematerials are encountered, definite con-sideration should be given to upgrading anotherwise unacceptable soil by stabilization.

The rapid method of mix design should beindicative of the type and percentage of stabi-lizer required and the required designthickness. This procedure is meant to be afirst-step type of approach and is by no meansconclusive. Better laboratory tests areneeded to evaluate strength and durabilityand should be performed in specific caseswhere time allows. Estimated time require-ments for conducting tests on stabilizedmaterial are presented in Table 9-17. Evenwhen stabilized materials are used, properconstruction techniques and control practicesare mandatory.

THICKNESS DESIGN PROCEDURESThe first paragraphs of this section give

the design engineer information concerningsoil stabilization for construction of theater-of-operations roads and airfields. The

information includes procedures for deter-mining soil’s suitability for stabilization anda means of determining the appropriate typeand amount of stabilizer to be used. The finalobjective in this total systematic approach isto determine the required design thicknesses.Depending on the type of facility and the AI orthe CBR of the unstabilized subgrade, thedesign procedure presented in this section al-lows determination of the required thicknessof an overlying structure that must be con-structed for each anticipated facility.

This basic structural design problem mayhave certain conventional overriding factors,


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such as frost action, that influence this re-quired thickness. The decision to stabilize ornot may be based on factors other than struc-tural factors, such as economy, availability ofstabilizer, and time. It must be realized thatsoil stabilization is not a cure for all militaryengineering problems. Proper use of thismanual as a guide allows, in some cases,reductions in required thicknesses. Theprimary benefit in soil stabilization is that itcan provide a means of accomplishing orfacilitating construction in situations inwhich environmental factors or lack ofsuitable materials could preclude or seriouslyhamper work progress. Through the properuse of stabilization, marginal soils can oftenbe transformed into acceptable constructionmaterials. In many instances, the quantity ofmaterials required can be reduced andeconomic advantages gained if the cost ofchemical stabilization can be offset by asavings in material transportation costs.

The structural benefits of soil stabilization,shown by increased load-carrying capability,are generally known. In addition, increasedstrength and durability also occur withstabilization.

Generally, lesser amounts of stabilizersmay be used for increasing the degree ofworkability of a soil without effectively in-creasing structural characteristics. Also,greater percentages may be used for increas-ing strength at the risk of being uneconomicalor less durable. Some of the informationpresented is intended for use as guidance onlyand should not supersede specific trial-proven methods or laboratory testing wheneither exists.

Primary considerations in determiningthickness design are those that involve thedecision to construct a single-layer or multi-layer facility, as discussed earlier. Themethod chosen depends on the type of con-struction. All permanent construction andmost multi layer designs should use thereduced thickness design procedure. Usuallythe single layer is of expedient design.

ROADSSpecific procedures for determining total

and/or layer thicknesses for roads are dis-


cussed below. The more expedient methodsare shown first, followed by more elaborateprocedures. Road classification is based onequivalent number 18-kip, single-axle, dual-wheel applications. Table 9-18 lists theclasses of roads.

Single-LayerFor each category of roads (Classes A

through E), a single design curve is presentedthat applies to all types of stabilization (seeFigures 9-12 through 9-14 and Figure 9-16,page 9-32). These curves indicate the totalpavement thickness required on an unstabil-ized subgrade over a range of subgradestrength values. It should be noted that eachcurve terminates above a certain subgradeCBR. This is because design strength criteriafor unsurfaced roads indicate that a naturalsoil of this appropriate strength could sustainthe traffic volume required of this category offacility without chemical stabilization. Thefollowing flow diagram indicates the use ofthese design procedures:

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On a single-layer road, a thin wearingcourse may be advisable to provide water-proofing and to offset the effects of tireabrasion.

MultilayerFor each road category, four design curves

are shown (see Figures 9-16 and 9-17 andFigures 9-18 and 9-19, page 9-34). These cur-ves indicate the total thickness required forpavements incorporating one of the followingcombinations of soil and stabilizer:

Lime and fine-g-rained soils.Asphalt and coarse-grained soils.Portland cement and coarse-graind soils.

Coarse- and fine-g-rained soils are definedaccording to the USCS. The curves presentedin Figures 9-16 and 9-17 and Figures 9-18

and 9-19, page 9-34, are applicable over arange of subgrade CBR values.

Individual layer thickness can be ac-complished using Table 9-19, page 9-35. Thistable indicates minimum base and wearingcourse thickness requirements for road Clas-ses A through E. Minimum surface coursethickness requirements are indicated for abase course with a strength of 50 to 100 CBR.If a stabilized soil layer is used as a subbase,the design base thickness is the total thick-ness minus the combined thickness of baseand wearing courses. If a stabilized layer isused as a base course over an untreated sub-grade, the design base thickness is the totalthickness minus the wearing course thick-ness. The following flow diagram showsthese procedures:


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Reduced thickness design factors, (see-Table 9-20 and Figure 9-20, page 9-36 ) shouldbe applied to conventional design thicknesswhen designing for permanent and nonex-pedient road and airfield design. The use ofstabilized soil layers within a flexible pave-ment provides the opportunity to reduce theoverall thickness of pavement structure re-quired to support a given load. To design apavement containing stabilized soil layers re-quires the application of equivalency factorsto a layer or layers of a conventionallydesigned pavement. To qualify for applicationof equivalency factors, the stabilized layermust meet appropriate strength anddurability requirements set forth in TM5-822-4/AFM 88-7, Chapter 4. An equivalen-cy factor represents the number of inches of aconventional base or subbase that can bereplaced by 1 inch of stabilized material.Equivalency factors are determined from—

Table 9-20 for bituminous stabilizedmaterials.Figure 9-20, page 9-36, for materialsstabilized with cement, lime, or acombination of fly ash mixed withcement or lime.

Selection of an equivalency factor from thetabulation depends on the classification ofthe soil to be stabilized. Selection of an

equivalency factor from Figure 9-20, page9-36, requires that the unconfined compres-sive strength, determined according to ASTMD1633, is known. Equivalency factors aredetermined from Figure 9-20, page 9-36, forsubbase materials only. The relationship es-tablished between abase and a subbase is 2:1.Therefore, to determine an equivalency factorfor a stabilized base course, divide the sub-base factor from Figure 9-20, page 9-36, by 2.See TM 5-330/AFM 86-3, Volume II for con-ventional design procedures.


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AIRFIELDSSpecific procedures for determining the

total and/or layer thicknesses for airfields arediscussed in the following paragraphs. Themore expedient methods are shown first, fol-lowed by more elaborate procedures.Airfields are categorized by their position onthe battlefield, the runway length, and thecontrolling aircraft. Table 9-21 lists aircraftcategories.

Single-LayerDesign curves for single-layer airfield con-

struction are in Figures 9-21 through 9-28,pages 9-38 through 9-44. In these figures

the controlling aircraft and design life incycles (one cycle is one takeoff and one land-ing) are indicated for each airfield cate-gory. The design curves are applicable for alltypes of stabilization over a range of subgradestrengths up to a maximum above whichstabilization would generally be unwar-ranted if the indicated material subgradestrength could be maintained. Design curvesare presented for typical theater-of-opera-tions gross weights for the controlling aircraftcategory. For a single-layer facility, a thinwearing course may provide waterproofing orminimize abrasion resulting from aircrafttires. The following flow diagram indicatesthese procedures:


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MultilayerIn the design of multilayer airfields, it is

first necessary to determine the total designthickness based on conventional flexiblepavement criteria. Then an appropriatereduction factor is applied for the particularsoil-stabilizer combination anticipated foruse. Determinations of individual layerthickness finalizes the design. Conventional

flexible pavement design curves and proce-dures may be found in TM 5-330/AFM 86-3,Volume II. After total thickness has beendetermined, a reduction factor is applied (seeTable 9-22 or 9-23, page 9-45). Individuallayer thicknesses can be determined usingTable 9-24, page 9-46, and procedures indi-cated for multi layer roads. The following flowdiagram indicates these design procedures:


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EXAMPLES OF DESIGNUse of the design criteria in this section can

best be illustrated by examples of typicaldesign situations.

Example 1The mission is to construct an airfield for

the logistical support of an infantry divisionand certain nondivision artillery units. Thefacility must sustain approximately 210takeoffs and landings of C-130 aircraft,operating at 150,000 pounds gross weight,along with operations of smaller aircraft. Be-cause of unsatisfactory soil strengthrequirements and availability of chemicalstabilizing agents, stabilization is to be con-sidered. The facility is also considered anexpedient single-layer design.

A site reconnaissance and a few soilsamples at the proposed site indicate the fol-lowing:

The natural strength is 8 CBR.It has a PI of 15.It has a LL of 30.Twenty percent passes a Number 200sleve.

Thirty percent is retained on a Num-ber 4 sieve.

The classification is (SC).

Using this information, a determinationcan be made from Figure 9-4, page 9-12, andTable 9-3, page 9-13, that the proper agent iscement, lime, or fly ash. The soil-lime pH testindicates that a lime content of 3 percent is re-quired to produce a pH of 12.4. Since the soilclassified as an (SC), an estimated cementcontent of 7 percent is selected from Table9-7, page 9-15. The fly ash ratio is 4 percentlime, 1 percent cement, 16 percent fly ash,and 79 percent soil. The characteristics of alladditives are then reviewed, and because ofpredicted cool weather conditions, cementstabilization is chosen.

The design thickness is then determined.The facility will be designed as a close battlearea 3,000’ airfield designed for 420 cycles of aC-130 aircraft. To determine the designthickness. Figure 9-1, page 9-7, is used. For asubgrade strength of 8 CBR and interpolatingbetween the 125,000- and 175,000-pound cur-ves, the required design thickness is 13 1/2inches.


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Example 2The mission is to provide a rear area 6)000’

airfield facility for C-5A aircraft operating at320,000 pounds gross weight. Time andmaterials indicate that a multilayer facilitycan be constructed using nonexpedientmethods. A site reconnaissance indicates thefollowing:

The natural strength is 5 CBR.It has a PI of 5.It has a LL of 35.Fifteen percent passes the Number200 sieve.Sixty percent is retained on the Num-ber 4 sieve.The classification is (GM).

Chemical stabilization is considered for theupper subgrade, but a supply of 100-CBRbase course material is available. An asphal-tic concrete wearing course will be used.Since the soil classified as (GM), either

bituminous, fly ash, or cement stabilization isappropriate (see Figure 9-4, page 9-12, andTable 9-3, page 9-13). Because of the lack ofadequate quantities of cement and fly ash,bituminous stabilization will be tried.

The material is termed “sand-gravelbitumen. ” Table 9-13, page 9-24, recom-mends either asphalt cutbacks or emulsions(considerable materials passing the Number200 sieve); since cutback asphalt is available,it will be used. It is anticipated that the in-place temperature of the sand will be about100 degrees Fahrenheit. (From Table 9-13,page 9-24, it can then be determined that thegrade of cutback to be used is MC-800. Fromthe equation given on page 9-23 and thegradation curve (not shown for the example),a preliminary design content of 6.7 percentasphalt is determined.) Design specimensare then molded and tested using the proce-dures indicated in TM 5-530. Comparing thetest results with the criteria given previously


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(a minimum of 500 pounds), it can be deter-mined that the upper subgrade can bestabilized with cutback asphalt. An optimumasphalt content of 6.5 percent is indicated.

The design thickness is then determined.(Only procedures for determining designthickness of a Type A runway area will be in-dicated.) Since the airfield is a rear-area6,000’ facility with the C-141 as the control-ling aircraft category and is a multilayerdesign, TM 5-330, Figure D-36 is used. A sub-grade strength of 5 CBR and a designthickness of 45 inches is required for a con-ventional pavement. Since soil stabilizationis involved, reduced thickness design is al-lowed. Table 9-20, page 9-35, shows that theequalizing factor for an asphalt-stabilizedsubbase of a (GM) soil is 2.00. Therefore, therequired thickness for the pavement, includ-ing the surface and base course, is 22.5inches.

To determine individual layer thicknesses,use Table 9-24. For a rear-area, 6,000’ air-field with the C-141 as the controlling aircraftand a 100 CBR base-course strength, the mini-mum surface-course and base coursethicknesses are 2 1/2 and 6 inches, respective-ly. Thus, the individual layer thicknesswould be as follows: surface course, 2 1/2 in-ches; 100-CBR base course, 6 inches; andstabilized upper subgrade, 14.0 inches.Another viable solution would be to stabilizethe base course also.

Example 3The mission is to quickly provide an ex-

pedient road of geometrical classificationbetween two organizational units. Only thein-place material can be stabilized. Thepreliminary site investigation indicates thefollowing:

The natural strength is 15 CBR.It has a PI of 15.It has a LL of 30.Sixty percent passes a Number 40sieve.Fifty-five percent passes a Number200 sieve.The classification is (CL).

Expedient design procedures indicate thatlime or cement stabilization is feasible (seeTable 9-3, page 9-13, and Figure 9-4 page9-12). Only lime is readily available, Designprocedures for a single-layer C1ass E road willbe used. Figure 9-6, page 9-20, is used todetermine the initial design lime content,Since the soil has a PI of 15 and 60 percentpassing the number 40 sieve, an estimatedlime content of 2 1/2 percent is selected. Fig-ure 9-15, page 9-32, indicates that therequired design thickness of stabilizedmaterial is 9 inches.

Example 4The mission is to construct a road between

two rear-area units. Time and material con-ditions allow nonexpedient procedures. Ahot-mix plant is available so that an asphalticconcrete wearing course can be applied. How-ever, the upper portion of the in-placematerial must be upgraded to provide asuitable base course. Geometric criteria indi-cate that a Class D multi layer road isrequired. A soil survey reveals the followingwith respect to the in-place material:

The average soil strength is 7 CBR.It has a PI of 9.It has a LL of 25.Thirty-seven percent passes the Num-ber 200 sieve.Forty-five percent passes the Number4 sieve (25 percent is smaller than0.05 mm, and 5 percent is smallerthan 0.005 mm).The classification is (GC).

Following procedures in Figure 9-4, page9-12, and Table 9-3, page 9-13, it is deter-mined that cement or lime-cement-fly ashstabilization will work with this soil; how-ever, fly ash is not available. The soil-cementlaboratory test (see TM 5-530) is run. Testresults indicate that a cement content of 6percent is required. Figure 9-18, page 9-34, in-dicates that a total pavement thickness of 12inches is required above the 7-CBR subgradefor a cement-stabilized, coarse-grained soil.A minimum base-course strength of 70 CBR isassumed. Table 9-18, page 9-30, indicatesthat a Class D road is designed for 4.7 x 107


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18-kip equivalent loads and a CBR of 50; a 4-inch asphaltic cement pavement and a10-inch cement-stabilized base are required.

Example 5The mission is to provide an expedient tac-

tical support area airfield for the operation ofapproximately 7,000 cycles of F-4C traffic.The single-layer design is selected. A sitereconnaissance reveals the following:

The natural strength is 4 CBR.It has a PI of 12.Eleven percent passes a Number 200sieve.Twenty percent retained on a Num-ber 4 sieve.Organic material occurs as a trace inthe soil samples.

Climatological data indicate a trend forsubfreezing weather, and full traffic must beapplied immediately upon completion. Or-dinarily, based on information from Figure9-4, page 9-12, and Table 9-3, page 9-13,either cement, lime, or fly ash stabilizationwould be the appropriate agent for this situa-tion and the soil would classify as an (SW-SM)borderline. With the constraints on curingtimes, soil stabilization would not be the ap-propriate method of construction. Anothermeans, possibly landing mats, must be con-sidered for the successful completion of themission.

Example 6The mission is to provide an expedient

Class E road between two organizational taskforces. The single-layer design is selected.The preliminary site investigation for a por-tion of the road indicates a natural soilstrength of 30 CBR. The design curve for thisroad classification, shows that a 30-CBR soilis adequate for the intended traffic and that itdoes not require any stabilization (see Figure9-15, page 9-32). Therefore, no soil samplingor testing is necessary. A problem area maylater arise from a reduction of strength, thatis, a large volume of rainfall or a dust problemon this particular road.

THEATER-OF-OPERATIONS AIRFIELDCONSIDERATIONS

In the theater of operations, the lack oftrained personnel, specialized equipment, ortime often eliminates consideration of manylaboratory procedures. The CBR and specialstabilization tests in particular will not beconsidered for these reasons. As a result,other methods for determining design pave-ment thicknesses have been developed usingthe AI (see TM 5-330/AFM 86-3, Volume II).This system is purely expedient and shouldnot replace laboratory testing and reducedthickness design procedures.

Functions of Soil StabilizationAs previously discussed, the three primary

functions of stabilization are—Strength improvement.Dust control.Waterproofing.

Use of Table 9-25 allows the engineer toevaluate the soil stabilization functions asthey relate to different types of theater-of-operations airfields. It is possible to easilysee the uses of stabilization for the traffic ornontraffic areas of airfields. This table,developed from Table 9-26, page 9-50, showsthe possible functional considerations forsituations where either no landing mat, alight-duty mat, or a medium-duty mat may beemployed. (Landing mats are discussed inTM 5-330/AFM 86-3, Volume II and TM5-33 7.) As an example of the use of this table,consider the construction of the “heavy lift inthe support area.”

Referring to the traffic areas, a certain min-imum strength is required for unsurfaced-soiloperations (that is, without a landing mat) orif either the light duty mat (LM) or themedium duty mat (MM) is used. If the exist-ing soil strength is not adequate, stabilizationfor strength improvement may be consideredeither to sustain unsurfaced operations or tobe a necessary base for the landing mat. Fur-ther, if no mat is used, stabilization might beneeded only to provide dust control and/or soil


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waterproofing. If a landing mat is used, how-ever, the functions of dust control and soilwaterproofing would be satisfied andstabilization need not be considered in anyevent. Possible stabilization functions fornontraffic areas have been shown in a similarmanner. For certain airfields, such as the“light lift in the battle area, ” no function forstrength improvement in either traffic or non-traffic areas is indicated. Such airfields havean AI requirement of 5 or more unsurfacedoperations (see Table 9-26, page 9-50). Siteselection should be exercised in most in-stances to avoid areas of less than a 5 AI. Forcertain airfields, such as the “tactical in thesupport area,“ a landing mater improved sur-facing always will be provided. Therefore a“no mat” situation pertains only to the non-traffic areas.

Design Requirementsfor Strength Improvement

Where stabilization for strength improve-ment is considered, certain basic designrequirements, in terms of strength and thick-ness of a stabilized soil layer on a givensubgrade, must be met. The strength andthickness requirements vary depending onthe operational traffic parameters andthe strength of the soil directly beneath thestabilized soil layer. Since the trafficparameters are known for each airfield type,a minimum strength requirement for the sta-bilized soil layer can be specified for eachairfield based on unsurfaced-soil criteria. Forany given subgrade condition, the thicknessof a minimum-strength, stabilized-soil layernecessary to prevent overstress of the sub-grade also can be determined. Table 9-27,page 9-52, gives design requirements for traf-fic and nontraffic areas of different airfieldtypes for which stabilization may be used forstrength improvement. As seen, the mini-mum-strength requirement in terms of AI is afunction only of the applied traffic for a par-ticular airfield and is independent of thesubgrade strength. However, the thickness isa direct function of the underlying subgradestrength.

Proper evaluation of the subg-rade is essen-tial for establishing thickness requirements.

In evaluating the subgrade for stabilizationpurposes, a representative AI strength profilemust be established to a depth that wouldpreclude the possibility of overstress in theunderlying subgrade. This depth variesdepending on the—

Airfield.Pattern of the profile itself.Manner of stabilization.

In this regard, the thickness data given inTable 9-27, page 9-52, can be used also to pro-vide guidance in establishing an adequatestrength profile. Generally, a profile to adepth of 24 inches is sufficient to indicate thestrength profile pattern. However, if adecrease in strength is suspected in greaterdepths, the strength profile should be ob-tained to no less than the thickness indicatedin Table 9-27, page 9-52, under the 5-6 sub-grade AI column for the appropriate airfield.

The use of Table 9-27, page 9-52, to estab-lish the design requirements for soilstabilization is best illustrated by the follow-ing example: Assume that a rear area 3,500’airfield is to be constructed and that a sub-grade AI evaluation has been made fromwhich a representative profile to a sufficientdepth can be established. One of threegeneral design cases can be considered de-pending on the shape of the strength profile.

The first case considers constantstrength with depth; therefore, the re-quired thickness is read directly fromTable 9-27, page 9-52, under the ap-propriate subgrade AI column. Thus,in the example, if a subgrade AI of 8is measured, the required thickness ofa stabilized soil layer if no landingmat were used would be 18 inches.The required minimum strength ofthis stabilized soil layer is an AI of15. If the light landing mat wereused, a 6-inch-thick layer with a min-imum AI of 10 would be required as abase overlying the subgrade AI of 8.The second case considers an increasein strength with depth; therefore, therequired thickness of stabilization


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may be considerably less than indi-cated in the table. For this example,assume that the AI increases withdepth as shown in Figure 9-29. A sta-bilized layer can be provided either bybuilding up a compacted base cm topof the existing ground surface or bytreating the in-place soil. Because ofthis, each situation represents asomewhat different design problem.

An in-place treatment is analogous toreplacing the existing soil to some depth withan improved quality material. Wherestrength increases with depth, the point atwhich thickness is compatible with thestrength at that particular point must bedetermined. This point can be determinedgraphically simply by superimposing a plot ofthe thickness design requirements versussubgrade AI (see Table 9-27) directly on thestrength profile plot. This procedure isshown in Figure 9-29. The depth at which thetwo plots intersect is the design thickness re-quirement for a stabilized-soil layer. In theexample, a thickness of 9.5 inches (or say 10inches) is required.

If a compacted base of a select borrow soil isused to provide a stronger layer on the sub-grade shown in Figure 9-29, the thicknessmust again be consistent with the strength atsome depth below the surface of the placedbase-course layer. Since the base-courselayer itself will be constructed to a minimumAI of 15, the weakest point under the placedbase will be at the surface of the existingground, or in this instance an AI of 8. Usingthis value, Table 9-27 gives a thickness of 18inches of base course. Compaction of the ex-isting ground would be beneficial in terms ofthickness requirements if it would increasethe critical subgrade strength to a highervalue. If, for example, the minimum AI of theexisting ground could be increased from 8 to12, the thickness of base required would bereduced to 10 inches (see Table 9-27).

The third case considers a decrease instrength with depth. The strengthprofile shown in Figure 9-30, page9-54 indicates a crust of firm material

over a significantly weaker zone ofsoil beneath. In this example, the impor-tance of proper analysis of subgradeconditions is stressed. If strength datawere obtained to less than 30 inches,the adequacy of the design could notbe fully determined.

Consider again an in-place stabilizationprocess. Although the strength profile anddesign curve intersect initially at a shallowdepth (about 3 inches) (see Figure 9-30, page9-54), the strength profile does not remain tothe right of the design curve. This indicatesthat the design requirement has been satis-fied. The second and final intersection occursat 24 inches. Since there is no indication of afurther decrease in strength with depth, athickness of 24 inches is therefore required.

In the case of a compacted base placed on asubgrade that decreases in strength withdepth, the procedure for determining thedesign thickness is more difficult. The designthickness can be determined by comparingthe strength-depth profile with the designcurve. If the measured AI at any given depthis less than the minimum requirement shownby the design curve, a sufficient thickness ofimproved quality soil must be placed on theexisting ground surface to prevent overstress


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at that depth. However, the thickness of basenecessary must be such that the require-ments will be met at all depths. To satisfythis condition, the required thickness must beequal to the maximum difference, which willoccur at a particular strength value, betweenthe depth indicated by the design curve andthe depth from the strength-depth profile, Inthe example shown in Figure 9-30, this max-imum difference occurs at an AI of 12. Thedifference is 10 inches, which is the requiredthickness for an improved quality base.

The same procedures described for adecrease in strength with depth can be usedto derive the strength and thickness require-ments for a base course under either an LM orMM. The thickness design requirementsgiven herein are for stabilized soil layershaving a minimum strength property to meetthe particular airfield traffic need. Although

the strength actually achieved may well ex-ceed the minimum requirement, noconsideration should be given to reducing thedesign thickness as given in Table 9-27, page9-52, or as developed by the stated proce-dures.

Section III. Dust Control

EFFECTS OF DUSTDust can be a major problem during combat

(and training) operations. Dust negativelyimpacts morale, maintenance, and safety.Experience during Operation DesertShield/Storm suggests that dust was a majorcontributor to vehicle accidents. It also ac-celerated wear and tear on vehicles andaircraft components.

Dust is simply airborne soil particles. As ageneral rule, dust consists predominantly ofsoil that has a particle size finer than 0.074mm (that is, passing a Number 200 sieve).

The presence of dust can have significantadverse effects on the overall efficiency ofaircraft by—

Increasing downtime and mainte-nance requirements.Shortening engine life.Reducing visibility.Affecting the health and morale ofpersonnel.

In addition, dust clouds can aid the enemy byrevealing positions and the scope of opera-tions.

DUST FORMATIONThe presence of a relative amount of dust-

size particles in a soil surface does notnecessarily indicate a dust problem nor theseverity of dust that will result in varioussituations. Several factors contribute to thegeneration, severity, and perpetuity of dustfrom a potential ground source. These in-clude—

Overall gradation.Moisture content.Density and smoothness of theground surface.


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Presence of salts or organic matter,vegetation, and wind velocity anddirection.Air humidity.

When conditions of soil and environmentare favorable, the position of an external forceto a ground surface generates dust that existsin the form of clouds of various density, size,and height above the ground. In the case ofaircraft, dust may be generated as a result oferosion by propeller wash, engine exhaustblast, jet-blast impingement, and the draft ofmoving aircraft. Further, the kneading andabrading action of tires can loosen particlesfrom the ground surface that may become air-borne.

On unsurfaced roads, the source of dustmay be the roadway surface. Vehicle trafficbreaks down soil structure or abrades gravelbase courses, creating fine-grained particlesthat readily become airborne when trafficked.

DUST PALLIATIVESThe primary objective of a dust palliative is

to prevent soil particles from becoming air-borne. Dust palliative may be required forcontrol of dust on nontraffic or traffic areas orboth. If a prefabricated landing mat,membrane, or conventional pavement surfac-ing is used in the traffic areas of an airfield,the use of dust palliative would be limited tonontraffic areas. For nontraffic areas, a pal-liative is needed that can resist the maximumintensity of air blast impingement by anaircraft or the prevailing winds. Where dustpalliative provide the necessary resistanceagainst air impingement, they may be totallyunsuitable as wearing surfaces. An impor-tant factor limiting the applicability of a dustpalliative in traffic areas is the extent of sur-face rutting that will occur under traffic. lfthe bearing capacity allows the soil surface torut under traffic, the effectiveness of a shal-low-depth palliative treatment could bedestroyed rapidly by breakup and subsequentstripping from the ground surface. Some pal-liatives tolerate deformations better thanothers, but normally ruts 1½ inches deepresult in the virtual destruction of any thinlayer or shallow depth penetration dust pal-liative treatment.

The success of a dust-control programdepends on the engineer’s ability to match adust palliative to a specific set of factors af-fecting dust generation. These factorsinclude—

Intensity of area use.Topography.Soil type.Soil surface features.Climate.

Intensity of Area UseAreas requiring dust-control treatments

should be divided into traffic areas based onthe expected amount of traffic. The threeclasses of traffic areas are—

Nontraffic.Occasional traffic.Traffic.

Nontraffic Areas. These areas requiretreatment to withstand air-blast effects fromwind or aircraft operations and are not sub-jected to traffic of any kind. Typicalnontraffic areas include—

Graded construction areas.Denuded areas around the peripheryof completed construction projects.Areas bordering airfield or heliportcomplexes.Protective petroleum, oil, and lubri-cant (POL) dikes.Magazine embankments or ammuni-tion storage barricades.Bunkers and revetments.Cantonment, warehouse, storage, andhousing areas, excluding walkwaysand roadways.Unimproved grounds.Areas experiencing wind-borne sand.

Occasional-Traffic Areas. Besides resist-ing helicopter rotor downwash, aircraftpropwash, and air blast from jet engines,these areas are also subjected to occasionaltraffic by vehicles, aircraft, or personnel.Vehicle traffic is limited to occasional, non-channelized traffic. Typical occasional-traffic areas include the following:

Shoulders and overruns of airfields.


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Shoulders, hover lanes, and peri-pheral areas of heliports and heli-pads.Nontraffic areas where occasionaltraffic becomes necessary.

Traffic Areas. Areas subjected to regularchannelized traffic by vehicles, aircraft, orpersonnel. Properly treated traffic areasresist the effects of air blasts from fixed- orrotary-wing aircraft. Typical traffic areas in-clude:

Roadways and vehicle parking areas.Walkways.Open storage areas.Construction sites.Runways, taxiways, shoulders, over-runs, and parking areas of airfields.Hover lanes and landing and parkingpads of heliports.Tank trails.

TopographyDust palliative for controlling dust on flat

and hillside areas are based on the expectedtraffic, but the specific palliative selected maybe affected by the slope. For example, a liquidpalliative may tend to run off rather thanpenetrate hillside soils, which degrades thepalliative’s performance.

Divide the area to be treated into flat andhillside areas. Flat is defined as an averageground slope of 5 percent or less, whilehillside refers to an average ground slopegreater than 5 percent. Particular areas canbe given special attention, if required.

Soil TypeSoil type is one of the key features used to

determine which method and material shouldbe used for dust control. Soils to be treated fordust control are placed into five generaldescriptive groupings based on the USCS.They are—

Silts or clays (high LL) (types (CH),(OH), and (MH)).Silts or clays (low LL) (types (ML),(CL), (ML-CL), and (OL)).

Sands or gravels (with fines) (types(SM), (SC), (SM-SC), (GM), (GC),(GM-GO, and (GW-GM)).Sands (with little or no fines) (types(SW-SM), (SP), and (SW)).Gravels (with little or no fines) (types(GP) and (GW)).

Soil Surface FeaturesSoil surface features refer to both the state

of compaction and the degree of soil satura-tion in the area to be treated. Loose surfaceconditions are suitable for treatment in non-traffic or occasional areas only. Firm surfaceconditions are suitable for treatment underany traffic condition.

Loose and Dry or Slightly Damp Soil. Thesurface consists of a blanket (¼ to 2 inchesthick) of unbound or uncompactedsoil, overlying a relatively firm subgrade andranging in moisture content from dry toslightly damp.

Loose and Wet or Scurry Soil. The surfacecondition consists of a blanket ( ¼ to 2 inchesthick) of unbound or uncompacted soil, over-lying a soft to firm subgrade and ranging inmoisture content from wet to slurry consis-tency. Soil in this state cannot be treateduntil it is dried to either a dry or slightly dampstate.

Firm and Dry or Slightly Damp Soil. Thesurface condition consists of less than a ¼-inch-thick layer of loose soil, ranging inmoisture content from dry to slightly dampand overlying a bound or compacted firm soilsubgrade.

Firm and Wet Soil. The surface conditionresembles that of the previous category. Thissoil must be dried to either a dry or slightlydamp state before it can be treated.

ClimateClimatic conditions influence the storage

life, placement, curing, and aging of dust pal-liative. The service life of a dust palliativemay vary with the season of the year. For ex-ample, salt solutions become ineffective


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during the dry season when the relativehumidity drops below 30 percent.

DUST-CONTROL METHODSThe four general dust-control-treatment

methods commonly used are—Agronomic.Surface penetrant.Admix.Surface blanket.

AgronomicThis method consists of establishing,

promoting, or preserving vegetative cover toprevent or reduce dust generation from ex-posed soil surfaces. Vegetative cover is oftenconsidered the most satisfactory form of dustpalliative. It is aesthetically pleasing,durable, economical, and considered to bepermanent. Some agronomic approachesto dust control are suitable for theater-of-operations requirements. Planning construc-tion to minimize disturbance to the existingvegetative cover will produce good dust-palliative results later.

Agronomic practices include the use of—Grasses.Shelter belts.Rough tillage.

Grounds maintenance management and fer-tilizing will help promote the development ofa solid ground cover. Agronomic methods arebest suited for nontraffic and occasional-traffic areas; they are not normally used intraffic areas.

Grasses. Seeding, sprigging, or soddinggrasses should be considered near theater-of-operations facilities that have a projecteduseful life exceeding 6 months. Combiningmulch with seed promotes quicker estab-lishment of the grass by retaining moisture inthe soil. Mulching materials include straw,hay, paper, or brush. When mulches arespread over the g-round, they protect the soilfrom wind and water erosion. Mulches are ef-fective in preventing dust generation onlywhen they are properly anchored. Anchoring

can be accomplished by disking or by applyingrapid curing (RC) bituminous cutbacks orrapid setting (RS) asphalt emulsions. Mulchis undesirable around airports and heliportssince it may be ingested into jet engines,resulting in catastrophic engine failure.

Shelter Belts. They are barriers formed byhedges, shrubs, or trees that are high anddense enough to significantly reduce windvelocities on the leeward side. Their place-ment should be at right angles to theprevailing winds. While a detailed discussionof shelter-belt planning is beyond the scope ofthis manual, shelter belts should be con-sidered for use on military installations andnear forward landing strips (FLS) con-structed for contingency purposes in austereenvironments (such as those constructed inCentral America).

Rough Tillage. This method consists ofusing a chisel, a lister, or turning plows to tillstrips across nontraffic areas. Rough tillageworks best with cohesive soils that form clods.It is not effective in cohesionless soils and, ifused, may contribute to increased dustgeneration.

Surface PenetrantThe surface penetration method involves

applying a liquid dust palliative directly tothe soil surface by spraying or sprinkling andallowing the palliative to penetrate the sur-face. The effectiveness of this methoddepends on the depth of penetration of thedust palliative (a function of palliative vis-cosity and soil permeability). Using water toprewet the soil that is to be treated enhancespenetration of the palliative.

Surface penetrants are useful under alltraffic conditions; however, they are only ef-fective on prepared areas (for example, onunsurfaced gravel roads). Dust palliativethat penetrate the soil surface include—

Bitumens.Resins.Salts.Water.


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Bitumens. Conventional types of bitu-minous materials that may be used for dustpalliative include—

Cutback asphalts.Emulsified asphalts.Road tars.Asphaltic penetrative soil binder(APSB).

These materials can be used to treat bothtraffic and nontraffic areas. All bituminousmaterials do not cure at the same rate. Thisfact may be of importance when they arebeing considered for use in traffic areas. Also,bituminous materials are sensitive toweather extremes. Usually bituminousmaterials impart some waterproofing to thetreated area that remains effective as long asthe treatment remains intact (for example, asplaced or as applied). Bituminous materialsshould not be placed in the rain or when rainis threatening.

A cutback asphalt (cutbacks) is a blend ofan asphalt cement and a petroleum solvent.These cutbacks are classified as RC, mediumcuring (MC), and slow curing (SC), dependingon the type of solvent used and its rate ofevaporation. Each cutback is further gradedby its viscosity. The RC and SC grades of 70and 250, respectively, and MC grades of 30,70, and 250 are generally used. Regardless ofclassification or grade, the best results are ob-tained by preheating the cutback. Sprayingtemperatures usually range from 120 to 300degrees Fahrenheit. The actual range for aparticular cutback is much narrower andshould be requested from the supplier at thetime of purchase. The user is cautioned thatsome cutbacks must be heated above theirflash point for spraying purposes; therefore,no smoking or open flames should be per-mitted during the application or the curing ofthe cutback. The MC-30 grade can besprayed without being heated if the tempera-ture of the asphalt is 80 degrees Fahrenheitor above. A slightly moist soil surface assistspenetration. The curing time for cutbacksvaries with the type. Under favorable groundtemperature and weather conditions, RCcures in 1 hour, MC in 3 to 6 hours, and SC in

1 to 3 days. In selecting the material for use,local environmental protection regulationsmust be considered.

Asphalt emulsions (emulsions) are a blendof asphalt, water, and an emulsifying agent.They are available either as anionic orcationic emulsions. The application of emul-sions at ambient temperatures of 80 degreesFahrenheit or above gives the best results.Satisfactory results may be obtained belowthis temperature, especially if the applicationis made in the morning to permit the warmingeffects of the afternoon sun to aid in curing.Emulsions should not be placed at tempera-tures below 50 degrees Fahrenheit.Emulsions placed at temperatures belowfreezing will freeze, producing a substandardproduct. For best results in a freezing en-vironment, emulsions should be heated tobetween 75 and 130 degrees Fahrenheit. Thetemperature of the material should never ex-ceed the upper heating limit of 185 degreesFahrenheit because the asphalt and waterwill separate (break), resulting in materialdamage. Emulsions generally cure in about 8hours. The slow setting (SS) anionic emul-sions of grades SS-1 and SS-lh may be dilutedwith 1 to 5 or more parts water to one partemulsified asphalt by volume before using.As a general rule, an application of 3 partswater to 1 part emulsion solution is satisfac-tory. The slow-setting cationic emulsions orgrades cationic slow setting (CSS)-1 and CSS-1h are easiest to use without dilution. Ifdilution is desired, the water used must befree of any impurities, minerals, or salts thatmight cause separation (breaking) of theemulsion within the distribution equipment.

Road tars (RTs) (tars) are viscous liquidsobtained by distillation of crude tars obtainedfrom coal. Tars derived from other basicmaterials are also available but are not nor-mally used as soil treatments. Tars aregraded by viscosity and are available ingrades ranging from 1 to 12. They are alsoavailable in the road tar cutback (RTCB) formof viscosity grades 5 and 6 and in the emul-sified form. Tar emulsions are difficult toprepare and handle, The low-viscositygrades RT-1 and RT-2 and the RTCB gradescan be applied at temperatures as low as 60


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degrees Fahrenheit without heating. The tarcutbacks generally have better penetratingcharacteristics than asphalts and normallycure in a few hours. Tars produce excellentsurfaces, but curing proceeds very slowly.Several days or even weeks may be requiredto obtain a completely cured layer. Tars aresusceptible to temperature changes and maysoften in hot weather or become brittle in coldweather.

APSB, a commercial product, is a specialliquid asphalt composed of a high penetrationgrade of asphalt and a solvent blend ofkerosene and naphtha. It is similar in char-acter to a standard low-viscosity, medium-curing liquid asphalt} but it differs in manyspecific properties. The APSB is suitable forapplication to soils that are relatively imper-vious to conventional liquid asphalts andemulsion systems. Silts and moderately plas-tic clays (to a PI of 15) can be treatedeffectively. Curing time for the APSB is 6 to12 hours under favorable ground tempera-ture and weather conditions. Onhigh-plasticity solids (with a PI greater than15), the material remains on the surface as anasphalt film that is tacky at a groundtemperature of approximately 100 degreesFahrenheit and above. The APSB must beheated to a temperature between 130 to 150degrees Fahrenheit to permit spraying withan asphalt distributor.

Resins. These dust palliative may be usedas either surface penetrants or surfaceblankets. They have a tendency to eitherpenetrate the surface or form a thin surfacefilm depending on the type of resin used, thesoil type, and the soil condition. Thematerials are normally applicable to nontraf-fic areas and occasional-traffic areas whererutting will not occur. They are not recom-mended for use with silts and clays.

Resin-petroleum-water emulsions arequite stable and highly resistant to weather-ing. A feature of this type of dust palliative isthat the soil remains readily permeable towater after it is treated. This type of productis principally manufactured under the tradename Coherex. Application rates range from

0.33 to 0.5 gallon per square yard. Thematerial may be diluted for spraying using 4parts water to 1 part concentrate. Thismaterial is primarily suited for dry sandysoils; it provides unsuitable results whenused on silty and clayey soils.

Lignin is a by-product of the manufactureof wood pulp. It is soluble in water and there-fore readily penetrates the soil. Its volubilityalso makes it susceptible to leaching from thesoil; thus, application is repeated as neces-sary after rainfall. Lignin is readily availablein the continental United States and certainother sections of the world. It is useful inareas where dust control is desirable for shortperiods of time; it is not recommended for usewhere durability is an important factor. Therecommended application rate is 1 gallon persquare yard of a resinous solution of 8 percentsolid lignin sulphite.

Concrete curing compounds can be used topenetrate sands that contain little or no siltsor clays. This material should be limited toareas with no traffic. The high cost of thismaterial is partly offset by the low applicationrate required (0.1 to 0.2 gallon per squareyard). Standard asphalt pressure dis-tributors can be used to apply the resin;however, the conventional spray nozzlesshould be replaced with nozzles with smalleropenings to achieve a uniform distribution atthe low application rate.

Salts. Salts in water emulsions have beenused with varying success as dust palliative.Dry calcium chloride (CaC12) is deliquescentand is effective when the relative humidity isabout 30 percent or greater. A soil treatedwith calcium chloride retains more moisturethan the untreated soil under comparabledrying conditions. Its use is limited tooccasional-traffic areas, Sodium chloride(NaC1) achieves some dust control by retain-ing moisture and also by some cementingfrom salt crystallization. Both calciumchloride and sodium chloride are soluble inwater and are readily leached from the soilsurface; thus, frequent maintenance is re-quired. Continued applications of salt


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solutions can ultimately build up a thin,crusted surface that will be fairly hard andfree of dust. Most salts are corrosive to metaland should not be stored in the vehicle usedfor application. Magnesium chloride(MgC12) controls dust on gravel roads withtracked-vehicle traffic. Best results can beexpected in areas with occasional rainfall orwhere the humidity is above 30 percent. Thedust palliative selected and the quantity usedshould not exceed local environmental protec-tion regulations.

Water. As a commonly used (but very tem-porary) measure for allaying dust, a soilsurface can be sprinkled with water. As longas the ground surface remains moist or damp,soil particles resist becoming airborne.Depending on the soil and climate, frequenttreatment may be required. Water shouldnot be applied to clay soil surfaces in suchquantity that puddles forms since a muddy orslippery surface may result where the soilremains wet.

AdmixThe admix method involves blending the

dust palliative with the soil to produce auniform mixture. This method requires moretime and equipment than either the penetra-tion or surface blanket methods, but it has thebenefit of increasing soil strength.

Normally, a minimum treatment depth of 4inches is effective for traffic areas and 3 in-ches for other areas. The admixture can bemixed in place or off site. Typical admixturedust palliative include—

Portland cement.Hydrated lime.Bituminous materials.

In-Place Admixing. In-place admixing isthe blending of the soil and a dust palliativeon the site. The surface soil is loosened (ifnecessary) to a depth slightly greater thanthe desired thickness of the treated layer.The dust palliative is added and blended withthe loosened surface soil, and the mixture iscompacted. Powders may be spread by handor with a mechanical spreader; liquids should

be applied with an asphalt distributor.Mixing equipment that can be used in-cludes—

Rotary tillers.Rotary pulverizer-mixers.Graders.Scarifies.Disk harrows.Plows.

Admixing and/or blending should continueuntil a uniform color of soil and dust palliativemixture, both horizontally and vertically, isachieved. The most effective compactionequipment that can be used is a sheepsfoot orrubber-tired rollers. The procedure for in-place admixing closely resembles the soilstabilization procedure for changing soilcharacteristics and soil strength used in roadconstruction. For dust control on a nontrafficarea, adequate compaction can be achieved bytrafficking the entire surface with a 5-tondual-wheel truck. For all other traffic situa-tions, the procedure should follow TM5-822-4. This procedure is time-consumingand requires the use of more equipment thanthe other three. Following placement, admix-ing, and compaction, a minimum of sevendays is required for curing.

Two cementing-type powders (portland ce-ment and hydrated lime) are primarily usedto improve the strength of soils. However,when they are admixed with soils in rela-tively small quantities (2 to 5 percent by drysoil weight), the modified soil is resistant todusting. Portland cement is generally suitedto all soil types, if uniform mixing can beachieved, whereas hydrated lime is ap-plicable only to soils containing a highpercentage of clay. The compacted soil sur-face should be kept moist for a minimum of 7days before allowing traffic on it.

Bituminous materials are more versatilethan cementing materials in providing ade-quate dust control and waterproofing of thesoil. Cutbacks, emulsion asphalts, and roadtars can all be used successfully. The quan-tity of residual bituminous material usedshould range from 2 to 3 percent of dry soil


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weight (for soils having less than 30 percentpassing the Number 200 sieve) to 6 to 8 per-cent (for soils having more than 30 percentfine-grained soils passing the Number 200sieve). The presence of mica in a soil isdetrimental to the effectiveness of a soil-bituminous material admixture. There areno simple guides or shortcuts for designingmixtures of soil and bituminous materials.The maximum effectiveness of soil-bituminous material admixtures can usuallybe achieved if the soil characteristics arewithin the following limits:

The PI is The amount of material passing theNumber 200 sieve is 30 percent byweight.

This data and additional construction datacan be found in TM 5-822-4. Traffic should bedetoured around the treated area until thesoil-bituminous material admixture cures.

Cutback asphalt provides a dust-free,waterproof surface when admixed into soil todepths of 3 inches or more on a firm subgrade.More satisfactory results are obtained if thecutback asphalt is preheated before using it.Soils should be fairly dry when cutback as-phalts are admixed. When using SC or MCtypes of cutback asphalt, aerate the soil-asphalt mixture to allow the volatiles toevaporate.

Emulsified asphalts are admixed with aconditioned soil that allows the emulsion tobreak before compaction. A properly condi-tioned soil should have a soil moisturecontent not to exceed 5 percent in soils havingless than 30 percent passing the Number 200sieve. Emulsified asphalts, particularly thecationics (CSS-1 or CSS-lb), are very sensi-tive to the surface charge of the aggregate orsoil. When they are used improperly, theemulsion may break prematurely or aftersome delay. The slow-setting anionic emul-sions of grades SS-1 and SS-lh are lesssensitive.

Road tars with RT and RTCB grades can beused as admixtures in the same manner as

10.

other bituminous materials. Road tar admix-tures are susceptible to temperature changesand may soften in hot weather or become brit-tle in cold weather.

Off-Site Admixing. Off-site admixing isgenerally used where in-place admixing is notdesirable and/or soil from another sourceprovides a more satisfactory treated surface.Off-site admixing may be accomplished witha stationary mixing plant or by windrow-mixing with graders in a central workingarea. Processing the soil and dust palliativethrough a central plant produces a moreuniform mixture than in-place admixing.The major disadvantage of off-site operationsis having to transport and spread the mixedmaterial.

Surface BlanketThe principle of the surface blanket method

is to place a “blanket” cover over the soil sur-face to control dust. The three types ofmaterials used to form the blanket are—

Minerals (aggregates).Synthetics (prefabricated membranesand meshes).Liquids (bituminous or polyvinyl ace-tate liquids).

These materials may be used alone or in thecombinations discussed later.

The type of treatment used dictates theequipment required. However, in all cases,standard construction equipment can be usedeffectively to place any of the blanketmaterials. Mechanized equipment should beused wherever possible to assure uniformityof treatment.

The surface blanket method is applicable tonontraffic, occasional-traffic, and trafficareas. Aggregate, prefabricated membrane,and mesh treatments are easy to place andcan withstand considerable rutting. Theother surface blanket methods onlywithstand considerable rutting. Once a sur-face blanket treatment is torn or otherwisecompromised and the soil exposed, sub-sequent traffic or air blasts increase the


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damage to the torn surface blanket andproduce dust from the exposed soil. Repairs(maintenance) should begin as soon as pos-sible to protect the material in place and keepthe dust controlled.

Minerals (aggregates). Aggregate is ap-propriate in arid areas where vegetativecover cannot be effectively established. It iseffective as a dust palliative on nontraffic andoccasional-traffic areas. The maximumrecommended aggregate size is 2 inches; ex-cept for airfields and heliports. To preventthe aggregate from being picked up by theprop (propeller) wash, rotor wash, or air blast,4-inch aggregate is recommended (see Table9-28).

Prefabricated Membrane. Membraneused to surface an area controls dust and evenacts as a surface course or riding surface fortraffic that does not rut the soil. When sub-jected to traffic, the membrane can beexpected to last approximately 5 years.Minor repairs can be made easily. For op-timum anchorage, the membrane should beextended into 2-foot-deep ditches at each edgeof the covered area; then it should be staked inplace and the ditches backfilled. Furtherdetails on the use and installation of prefabri-cated membranes can be obtained from TM5-330/AFM 86-3, Volume II.

Prefabricated Mesh. Heavy, woven jutemesh, such as commonly used in conjunctionwith grass seed operations, can be used fordust control of nontraffic areas. The meshshould be secured to the soil by burying the

edges in trenches and by using large U-shaped staples that are driven flush with thesoil surface. A minimum overlap of 3 inchesshould be used in joining rolls of mesh;covered soil should be sprayed with abituminous material. Trial applications arerecommended at each site and should be ad-justed to suit each job situation.

Bituminous Liquid. Single- or double-bituminous surface treatments can be used tocontrol dust on most soils. A medium-curingliquid asphalt is ordinarily used to prime thesoil before placing the surface treatment.Fine-grained soils are generally primed withMC-30 and coarse-grained soils with MC-70.After the prime coat cures, a bituminousmaterial is uniformly applied, and gravel,slag, or stone aggregate is spread over thetreated area at approximately 25 pounds persquare yard. The types of bituminousmaterials, aggregate gradations, applicationrates, and methods of placing surface treat-ments are described in TM 5-822-8/AFM88-6, Chapter 9. Single-or double-bituminoussurface treatments should not be used whereturf is to be established.

Polyvinyl Acetate (DCA 1295) (withoutreinforcement). DCA 1295 has a slight odorand an appearance similar to latex paint.The material is diluted 3 parts DCA 1295 to 1.part water and cures in 2 to 4 hours underideal conditions of moderate to high tempera-ture and low relative humidity. A clear,flexible film forms on the treated surface.DCA 1295 can be sprayed with a conventionalasphaIt distributor provided modificationsare made to the pump to permit external


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lubrications. The DCA 1295 can be usedalone or over a fiberglass reinforcement. Ad-ding fiberglass does not affect the basicapplication procedures or the curing charac-teristics of the DCA 1295. This material issuitable for use on nontraffic, occasional-traffic, and traffic areas. It is also effectivewhen sprayed over grass seed to protect thesoil until grass occurs. Uniform soil coverageis enhanced by sprinkling (presetting) thesurface with water.

Polyvinyl Acetate (DCA 1295) (with rein-forcement). A fiberglass scrim material isrecommended for use with the DCA 1295when a reinforcement is desired. Fiberglassscrirn increases the expected life of the dust-control film by reducing the expansion andcontraction effects of weather extremes. Thescrim material should be composed offiberglass threads with a plain weave patternof 10 by 10 (ten threads per inch in the warpdirection and 10 threads per inch in the filldirection) and a greige finish. It should weighapproximately 1.6 ounces per square yard.Using scrim material does not create anyhealth or safety hazards, and special storagefacilities are not required. Scrim materialscan be applied under any climatic conditionssuitable for dispensing the DCA 1295.(Under special conditions, continuousstrands of fiberglass maybe chopped into l/2-inch-long segments and blown over the areato be protected.) The best method of place-ment is for the fiberglass scrim material to beplaced immediately after presetting withwater, followed by the DCA 1295.

Polypropylene-Asphalt Membrane. Thepolypropylene-asphalt membrane is recom-mended for use in all traffic areas. It hasconsiderable durability and withstands rut-ting up to approximately 2 inches in depth.This system is a combination of apolypropylene fabric sprayed with an asphaltemulsion. Normally a cationic emulsion isused; however, anionic emulsions have alsobeen used successfully. Several types ofpolypropylene fabric are commercially avail-able.

This treatment consists of the followingsteps:

Place a layer of asphalt (0.33 to 0.50gallon per square yard) on theground, and cover this with a layerof polypropylene fabric.Place 0,33 gallon per square yard ofasphalt on top of the polypropylene.Apply a sand-blotter course.

This system does not require any rolling orfurther treatment and can be trafficked imm-ediately.

Care should be taken during constructionoperations to ensure adequate longitudinaland transverse laps where two pieces ofpolypropylene fabric are joined. Lon-gitudinal joints should be lapped a minimumof 12 inches. On a superelevated section, thelap should be laid so the top lap end is facingdownhill to help prevent water intrusionunder the membrane. On a transverse joint,the minimum overlap should beat least 24 in-ches. Additional emulsion should be on thetop side of the bottom lap to provide enoughemulsion to adhere to and waterproof the toplap. Figure 9-31, page 9-64, illustrates thisprocess on tangential sections. Applyingpolypropylene on roadway curves requirescutting and placing the fabric as shown inFigure 9-32, page 9-64. The joints in curvedareas should be overlapped a minimum of 24inches.

SELECTION OF DUST PALLIATIVEThere are many dust palliative that are ef-

fective over a wide range of soils and climaticconditions. Engineering judgment andmaterial availability play key roles in deter-mining the specific dust palliative to select.Tables 9-29 through 9-32, pages 9-65 through9-70, were developed from evaluation of theiractual perform ante to assist in the selectionprocess. The dust palliative and dust controlmethods are not listed in any order of effec-tiveness.

Where no dust palliative is listed for a par-ticular dust control method, none was found


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to be effective under those conditions. For ex-ample, for the agronomic method, a dustpalliative is not recommended for a loose,sandy soil with no binder, nor is a dust pallia-tive recommended for the surface penetrationof a firm, clay soil (see Table 9-29, page 9-65and Table 9-30, page 9-66). Also, theagronomic method of dust control is notrecommended for any traffic area (see Table9-31, page 9-67).

In Table 9-32, page 9-68 through 9-70, num-bers representing dust palliative are listedin numerical order and separated by the dust-control method. This table includes the sug-gested rates of application for each dust-palliative; for instance, gallon per squareyard for liquid spray on applications or gallonper square yard per inch for liquid (or poundper square yard per inch for powders) admixapplications.

Application RatesThe application rates should be considered

estimates, as stated above. Unfortunately,the admix method and some surface-blanketmethods represent a full commitment.Should failure occur after selection and place-ment, the only recourse is to completelyretreat the failed area, which is a lengthy andinvolved process. However, should failureoccur on a section treated with a liquid dust

palliative, retreatment of the failed area isrelatively simple, involving only a distributorand operator. A second application is en-couraged as soon as it is determined that theinitial application rate is not achieving thedesired results.

PlacementNo treatment is suggested for areas con-

taining large dense vegetation and/or largedebris. Loose soil in a wet or slurry conditionand firm soil that is wet should not be treated.Dust problems should not exist in any of theseareas; however, if the areas are known dustproducers when dry, they should be dried orconditioned and then treated.

DilutionSeveral dilution ratios are mentioned for

some liquid dust palliatives. The ratios arepresented as volume of concentrate to volumeof water and should be viewed as a necessaryprocedure before a particular liquid can besprayed. The water is a necessary vehicle toget the dust palliative on the ground. Thestated application rate is for the dust pallia-tive only. When high dilution ratios arerequired to spray a dust palliative, extra careshould be taken to prevent the mixture fromflowing into adjacent areas where treatmentmay be unnecessary and/or into drainageditches. Two or more applications may be


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necessary to achieve the desired applicationrate. Considerable time can be saved by firstdetermining the minimum dilution that per-mits a dust palliative to be sprayed.

PrewettingAll liquid dust palliative present a better

finished product when they are sprayed overan area that has been prewet with water. Theactual amount of water used in presetting anarea varies but usually ranges from 0.03 to0.15 gallons per square yard. The watershould not be allowed to pond on the surface,and all exposed soil should be completelydampened. The performance of brinematerials is enhanced by increasing theamount of water to two to three times theusual recommendation. However, the watershould not be allowed to pond, and the fine-sized particles should not be washed away.

CuringMost liquid dust palliative require a

curing period. DCA 1295 dries on the soilsurface to form a clear film. The curing timeis around 4 hours but may vary withweather conditions. Brine materials do notrequire a curing period, making them imme-diately available to traffic. Bituminousmaterials may be ready to accept traffic assoon as the material temperature drops tothe ambient temperature.

DUST CONTROL ON ROADSAND CANTONMENT AREAS

Controlling dust on roads and in andaround cantonment areas is important inmaintaining health, morale, safety, andspeed of movement. Table 9-33, page 9-72,lists several dust palliative suitable for con-trolling dust on roads and in cantonmentareas, the equipment required to apply thepalliative, the level of training required, andthe life expectancy of the dust palliative.

DUST CONTROL FOR HELIPORTSDust control for heliports is essential for

safety reasons. Because of the nature ofheliborne operations, many aircraft are likelyto be arriving or departing simultaneously.Obscuration of the airfield due to dustreduces air traffic controllers’ ability to

control flight operations and represents a sig-nificant safety hazard. Adequate dustcontrol for the heliport is essential for safeand efficient flight operations. Figure 9-33,page 9-73, illustrates heliport areas requiringdust control and lists the dimensions of theareas to be treated based on aircraft type,Table 9-34, page 9-74, lists dust palliativesuitable for use around helipads and aircraftmaintenance areas.

C0NTROL OF SANDOperation Desert Storm highlighted the

problems of stabilizing airborne and migrat-ing sand. Airborne sand reduces the lifeexpectancy of mechanical parts exposed to itsabrasive effects. From a constructionstandpoint, migrating sand poses a sig-nificant engineering problem— how toprevent dune formation on facilities.

There are many ways to control migratingsand and prevent sand-dune formation onroads, airfields, and structures. There arecertain advantages and disadvantages ineach one. The following methods for thestabilization and/or destruction of wind-borne sand dunes are the most effective:

Fencing.Paneling.Bituminous materials.Vegetative treatment.Mechanical removal.Trenching.Water.Blanket covers.Salt solutions.

These methods may be used singularly or incombination.

FencingThis method of control employs flexible,

portable, inexpensive fences to destroy thesymmetry of a dune formation. The fencedoes not need to be a solid surface and mayeven have 50 percent openings, as in snowfencing. Any material, such as wood slats,slender poles, stalks, or perforated plasticsheets, bound together in any manner and at-tached to vertical or horizontal supports isadequate. Rolled bundles that can be


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transported easily are practical. Prefabri-cated fencing is desirable because it can beerected quickly and economically. Becausethe wind tends to underscore and underminethe base of any obstacle in its flow path, thefence should be installed about 1 foot aboveground level. To maintain the effectivenessof the fencing system, a second fence shouldbe installed on top of the first fence on thecrest of the sand accumulation. The entirewindward surface of the dune should be stabi-lized with a dust-control material, such asbituminous material, before erecting the firstfence. The old fences should not be removedduring or after the addition of new fences,Figure 9-34 shows a cross section of a stabi-lized dune with porous fencing. As long as thefences are in place, the sand remains trapped.If the fences are removed, the sand soonmoves downwind, forming an advancingdune. The proper spacing and number of fen-ces required to protect a specific area can onlybe determined by trial and observation. Fig-ure 9-35 illustrates a three-fence method ofcontrol. If the supply of new sand to the dune

is eliminated, migration accelerates and dunevolume decreases. As the dune migrates, itmay move great distances downwind before itcompletely dissipates. An upwind fence maybe installed to cut off the new sand supply ifthe object to be protected is far downwind ofthe dune. This distance usually should beatleast four times the width of the dune.

PanelingSolid barrier fences of metal, wood, plastic,

or masonry can be used to stop or divert sandmovement. To stop sand, the barriers shouldbe constructed perpendicular to the winddirection. To divert sand, the panels shouldbe placed obliquely or nearly parallel to thewind. They may be a single-slant or V-shapedpattern (see Figure 9-36, page 9-76). Whenfirst erected, paneling appears to give excel-lent protection. However, panels are notself-cleaning, and the initial accumulationsmust be promptly removed by mechanicalmeans. If the accumulation is not removed,sand begins to flow over and around the


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barrier and soon submerges the object to beprotected. Mechanical removal is costly andendless. This method of control is unsatisfac-tory because of the inefficiency and expense.It should be employed only in conjunctionwith a more permanent control, such asplantings, fencing, or dust palliative. Equal-ly good protection at less cost is achieved withthe fencing method.

Bituminous MaterialsDestroying dune symmetry by spraying

bituminous materials at either the center orthe ends of the dune is an inexpensive andpractical method of sand control. Petroleumresin emulsions and asphalt emulsions are ef-fective. The desired stickiness of the sand isobtained by diluting 1 part petroleum resinemulsion with 4 parts waters and spraying atthe rate of 1/2 gallon per square yard.Generally, the object to be protected should bedownwind a distance of at least twice the tip-to-tip width of the dune. The center portion ofa barchan dune can be left untreated, or it canbe treated and unstabilized portions allowedto reduce in size by wasting. Figure 9-37shows destruction of a typical barchan duneand stabilization depending on the areatreated.

Vegetative TreatmentEstablishing a vegetative cover is an excel-

lent method of sand stabilization. Thevegetation to be established must often bedrought resistant and adapted to the climate


and soil. Most vegetative treatments are ef-fective only if the supply of new sand is cut off.An upwind and water, fertilizers, and mulchare used liberally. To prevent the engulfmentof vegetation, the upwind boundaries areprotected by fences or dikes, and the seed maybe protected by using mulch sprayed with abituminous material. Seed on slopes maybeanchored by mulch or matting. Oats andother cereal grasses may be planted as a fast-growing companion crop to provide protectionwhile slower-growing perennial vegetationbecomes established. Usually the procedureis to plant clonal plantings, then shrubs (as anintermediate step), followed by long-livedtrees. There are numerous suitable vegeta-tive treatments for use in differentenvironments. The actual type of vegetationselected should be chosen by qualified in-dividuals familiar with the type of vegetationthat thrives in the affected area. Stabiliza-tion by planting has the advantages ofpermanence and environmental enhance-ment wherever water can be provided forgrowth.

Mechanical RemovalIn small areas, sand maybe removed by

heavy equipment. Conveyor belts and power-driven wind machines are not recommendedbecause of their complexity and expense.Mechanical removal may be employed onlyafter some other method has been used toprevent the accumulation of more deposits.Except for its use in conjunction with another

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method of control, the mechanical removal ofsand is not practical or economical.

TrenchingA trench maybe cut either transversely or

longitudinally across a dune to destroy itssymmetry. If the trench is maintained, thedune will be destroyed by wastage. Thismethod has been used successfully in theArizona Highway Program in the YumaDesert, but it is expensive and requires con-stant inspection and maintenance.

WaterWater may be applied to sand surfaces to

prevent sand movement. It is widely usedand an excellent temporary treatment.Water is required for establishing vegetativecovers. Two major disadvantages of thismethod are the need for frequent reapplica-tion and the need for an adequate andconvenient source.

Blanket CoversAny material that forms a semipermanent

cover and is immovable by the wind serves tocontrol dust. Solid covers, though expensive,provide excellent protection and can be usedover small areas. This method of sand controlaccommodates pedestrian traffic as well as aminimum amount of vehicular traffic.Blanket covers may be made from bituminousor concrete pavements, prefabricated landing

mats, membranes, aggregates, seashells, andsaltwater solutions. After placement of anyof these materials, a spray application ofbituminous material may be required toprevent blanket decomposition and sub-sequent dust.

Salt SolutionsWater saturated with sodium chloride or

other salts can be applied to sand dunes tocontrol dust. Rainfall leaches salts from thesoil in time. During periods of no rainfall andlow humidity (below approximately 30 per-cent), water may have to be added to thetreated area at a rate of 0.10 to 0.20 gallon persquare yard to activate the salt solution.

Section IV. ConstructionProcedures

MECHANICAL SOIL STABILIZATIONThis section provides a list of construction

procedures, using mechanical stabilizationmethods, which will be useful to the engineerin the theater of operations.

On-Site BlendingOn-site blending involves the following

steps:

Preparation.Shape the area to crown and grade.


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Scarify, pulverize, and adjust themoisture content of the soil, if neces-sary.Reshape the area to crown and grade.

Addition of Imported Soil Materials. Useone of the following methods:

Distribute evenly by means of an im-proved stone spreader.Use spreader boxes behind dumptrucks.Tailgate each measured truck, load-ing to cover a certain length.Dump in equally spaced piles, thenform into windrows with a motorgrader before spreading.

Mixing.Add water, if required, to obtain amoisture content of about 2 percentabove optimum and mix with either arotary mixer, pulvimixer, blade, scari-fier, or disk.Continue mixing until the soil and ag-gregate particles are in a uniform,well-graded mass.Blade to crown and grade, if needed.

Compaction.Compact to specifications determinedby the results of a CE 55 Proctor testperformed on the blended soil ma-terial.Select the appropriate type(s) of com-paction equipment, based on the gra-dation characteristics of the blendedsoil.

Off-Site BlendingOff-site blending involves the following

steps:

Preparation. Shape area to crown andgrade.

Addition of Blended Soil Materials.Spread blended material evenly,using one of the methods discussedfor on-site blending.


Determine the moisture content ofthe placed, blended material. Adjustthe moisture content, if necessary.

Lime StabilizationLime stabilization involves the following

steps:

Preparation.Shape the surface to crown andgrade.Scarify to the specified depth.Partially pulverize the soil.

Spreading. Select one of the followingmethods; use about 1/2 of the total lime re-quired.

Spot the paper bags of lime on therunway, empty the bags, and levelthe lime by raking or dragging.Apply bulk lime from self-unloadingtrucks (bulk trucks) or dump truckswith spreaders.Apply the lime by slurry (1 ton of limeto 500 gallons of water). The slurrycan be mixed in a central plant or in atank truck and distributed by stand-ard water or asphalt tank trucks withor without pressure.

Preliminary Mixing, Watering, andCuring.

Mix the lime and soil (pulverize soilto less than a 2-inch particle size ex-clusive of any gravel or stone).Add water.

CAUTIONThe amount of water need to be in-creased by approximately 2 percent forlime stabilization purposes.

Mix the lime, water, and soil usingrotary mixers (or blades).Shape the lime-treated layer to theapproximate section.Compact lightly to minimize evapora-tion loss, lime carbonation, or exces-sive wetting from heavy rains.

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Cure lime-soil mixture for zero to 48hours to permit the lime and water tobreak down any clay clods. For ex-tremely plastic clays, the curingperiod may be extended to 7 days.

Final Mixing and Pulverization.Add the remaining lime by the ap-propriate method.Continue the mixing and pulveriza-tion until all of the clods are brokendown to pass a l-inch screen and atleast 60 percent of the material willpass a Number 4 sieve.Add water, if necessary, during themixing and pulverization process.

Compaction.Begin compaction immediately afterthe final mixing.Use pneumatic-tired or sheepsfootrollers.

Final curing.Let cure for 3 to 7 days.Keep the surface moist by periodicallyapplying an asphaltic membrane orwater.

Cement StabilizationCement stabilization involves the following

steps:

Preparation.Shape the surface to crown andgrade.Scarify, pulverize, and prewet thesoil, if necessary.Reshape the surface to crown andgrade.

Spreading. Use one of the followingmethods:

Spot the bags of cement on the run-way, empty the bags, and level the ce-ment by raking or dragging.Apply bulk cement from self-unloading trucks (bulk trucks) ordump trucks with spreaders.

Mixing.Add water and mix in place with arotary mixer.Perform by processing in 6- to8-foot-wide passes (the width ofthe mixer) or by mixing in a windrowwith either a rotary mixer or motorgrader.

Compaction.Begin compaction immediatelythe final mixing (no more than 1should pass between mixingcompaction), otherwise cementhydrate before compactioncompleted.

after hourand

mayis

Use pneumatic-tired and sheepsfootrollers. Finish the surface withsteel-wheeled rollers.

Curing. Use one of the following methods:Prevent excessive moisture loss byapplying a bituminous material at arate of approximately 0.15 to 0.30gallon per square yard.Cover the cement with about 2 inchesof soil or thoroughly wetted straw.

Fly-Ash StabilizationThe following construction procedures for

stabilizing soils apply to fly ash, lime-fly ashmixtures, and lime-cement-fly ash mixtures:

Preparation.Shape the surface to crown andgrade.Scarify and pulverize the soil, ifnecessary.Reshape the surface to crown andgrade.

Spreading. Use one of the following:

Spot the bags of fly ash on the road orairfield; empty the bags intoindividual piles; and distribute the flyash evenly across the surface with arake or harrow.Apply fly ash or a fly ash mixture inbulk from self-unloading trucks (bulk


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trucks) or dump trucks withspreaders.

Mixing.Begin mixing operations within 30minutes of spreading the fly ash.Mix the soil and fly ash thoroughly byusing a rotary mixer, by windrowingwith a motor grader, or by using adisk harrow.Continue to mix until the mixtureappears uniform in color.

Compaction.Add water to bring the soil moisturecontent to 2 percent above the OMC.Begin compaction immediately follow-ing final mixing. Compaction must becompleted within 2 hours of mixing.Minimum compactive effort for soilstreated with fly ash is 95 percent ofthe maximum dry density of themixed material.Reshape to crown and grade; thenfinish compaction with steel-wheeledrollers.

Curing. After the fly ash treated lifts havebeen finished, protect the surface from dryingto allow the soil material to cure for not lessthan 3 days. This maybe accomplished by—

Applying water regularly throughoutthe curing period.Covering the amended soil with a 2-inch layer of soil or thoroughly wettedstraw.Applying a bituminous material atthe rate of approximately 0.15 to 0.30gallon per square yard.

Bituminous StabilizationIn-place stabilization using bituminous

materials can be performed with a travelingplant mixer, a rotary-type mixer, or a blade.The methods for using these mixers are out-lined below:

TravelingShapwhich

Want Mixer.and compact the roadbed onthe mixed material is to be

placed. A prime coat should be ap-plied on the roadbed and allowed tocure. Excess asphalt from the primecoat should be blotted with a light ap-plication of dry sand.Haul aggregate to the job and wind-rowed by hauling trucks, a spreaderbox, or a blade.Add asphalt to the windrow by anasphalt distributor truck or addedwithin the traveling plant mixer.Use one of the several types ofsingle- or multiple-pass shaft mixersthat are available.Work the material until about 50percent of the volatiles have escaped.A blade is often used for thisoperation.Spread the aggregate to a uniformgrade and cross section.Compact.

Rotary Mixer.Prepare the roadbed as explainedabove for the traveling plant mixer.Spread the aggregate to a uniformgrade and cross section.Add asphalt in increments of about0.5 gallon per square yards and mix.Asphalt can be added within themixer or with an asphalt distributortruck.Mix the aggregate by one or morepasses of the mixer.Make one or more passes of the mixerafter each addition of asphalt.Maintain the surface to the grade andcross section by using a blade duringthe mixing operation.Aerate the mixture.

Blade Mixing.Prepare the roadbed as explainedabove for the traveling plant mixer.Place the material in a windrow.Apply asphalt to the flattenedwindrow with a distributor truck. Amultiple application of asphalt couldbe used.Mix thoroughly with a blade.Aerate the mixture.


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Move the mixed windrow to one sideof the roadway.Spread the mixture to the propergrade and crown.Compact the mixture.

Central Plant Construction MethodsAlthough central plant mixing is desirable

in terms of the overall quality of the stabilizedsoil, it is not often used for theater-of-operations construction. Stabilization withasphalt cement, however, must be ac-complished with a central hot-mix plant.

The construction methods for central plantmixing that are common for use with all typesof stabilizers are given below:

Storing.Prepare storage areas for soils andaggregates.Prepare storage area for stabilizer.Prepare storage area for water.

Mixing.Prepare the area to receive thematerials.Prepare the mixing areas.

Hauling. Use trucks.

Placing. Use a spreader box or bottom -dump truck, followed by a blade to spread to auniform thickness.

Compacting. Use a steel-wheeled,pneumatic-tired, or sheepsfoot roller,depending on the material.

Curing. Provide an asphaltic membrane forcement-stabilized soil and an asphalticmembrane or water for lime-stabilized soils.

Surface WaterproofingSurface waterproofing involves the follow-

ing steps:

Preparation.Shape the area to crown and grade.Remove all deleterious materials,such as stumps, roots, turf, andsharp-edged soil-aggregate particles.

Mixing.Adjust the water content to about op-timum to 2 percent below optimum,and mix with a traveling mixer, pul-vimixer, blade, scarifier, or plow.Blade to the crown and grade.

Compaction.Begin compaction after mixing.Use pneumatic-tired or sheepsfootrollers.

Membrane Placement.Grade the area to the crown andgrade and cut anchor ditches.Use a motor grader.Roll the area with a steel-wheeledroller or a lightweight, pneumatic-tired roller.Place a neoprene-coated nylon fabricor a polypropylene-asphalt membraneon the area.


Documents

CHAPTER 9 Soil Stabilization for Roads and Airfields · FM 5-410 CHAPTER 9 Soil Stabilization for Roads and Airfields Soil stabilization is the alteration of one or more soil properties,