Jagadanand JhaGuru Nanak Dev Engineering College, Ludhiana

141006, India&

Sanjay Kumar ShuklaEdith Cowan University, Perth, WA 6027,

Australia

Compaction

Laboratory Test

Field Compaction

Case Study

Derivation for Field Compaction

The most commonly used ground improvement technique, where the soil is densified through external compactive effort/mechanical means by reducing volume of air.

Compactive Effort

+ water =

•To refill an excavation, or a void adjacent to a structure (such as behind a retaining wall.)•To provide man-made ground to support a structure•As a sub-base for a road, railway or airfield runway.•As a structure in itself, such as an embankment or earth dam, including reinforced earth

Improvement Effect on mass fill

Higher shear strength Greater stability

Lower compressibility Less settlement under state load

Higher CBR value Less deformation under repeated

Lower permeability Less tendency to absorb water

Lower frost susceptibility Less likelihood of frost heave

water

Solid Solid

Water

Load

Soil Matrix

Air Air

Vol. = VT1

Vol. = VT2

Compressed Soil

soil (2)> soil (1)

d, max

optimum water content

Zero Air Void

CurveSr =100%

Compaction Curve

Soil Compaction in the Lab:

1- Standard Proctor Test2- Modified Proctor Test3- Gyratory Compaction

Standard Proctor Test Modified Proctor Test

Soil Compaction in the Lab:

1- Standard Proctor Test

wc1 wc2 wc3wc4

wc5

d1 d2 d3d4

d5

OptimumWater

Content

WaterContent

Dry Density

d max

Zero Air Void CurveSr =100%

CompactionCurve

1

2

3

4

5

(OWC)

4 inch diameter compaction mold.(V = 1/30 of a cubic foot)

5.5 pound hammer

25 blowsper layer

H = 12 in

Wet toOptimum

Dry toOptimum

Increasing Water Content

e

G wsdry

1

dry =wet

Wc

100%1+

ZAV =Gs w

WcGs1+Sr

Soil Compaction in the Lab:

1- Standard Proctor TestASTM D-698 or AASHTO T-99

2- Modified Proctor TestASTM D-1557 or AASHTO T-180

Energy = 12,375 foot-pounds per cubic foot

Energy = 56,520 foot-pounds per cubic foot

Number of blows per layer x Number of layers x Weight of hammer x Height of drop hammer

Volume of moldEnergy =

MoistureContent

Dry Density

d max

CompactionCurve for StandardProctor

(OMC)

d max

(OMC)

Zero Air Void CurveSr < 100%

Zero Air Void CurveSr =100%

Zero Air Void CurveSr = 60%

CompactionCurve for ModifiedProctor

•Type of soil•Compactive effort•Effect of soil Structure / water Content•Organic content

Type of clay

Effect of clay content on density (Das 2006)

Proctor compaction test on Sand

Water Content

Dry Density

Effect of Energy on Soil Compactio (Compactive Effort)

HigherEnergy

ZAV

Increasing compaction energy Lower OWC and higher dry density

In the fieldincreasing compaction energy = increasing number of passes or reducing lift depth

In the labincreasing compaction energy = increasing

number of blows

Dry side of optimum- Flocculated structure and wet side of optimum- Dispersed structure

Higher compactive effort or water content give more dispersed fabric

Cohesive Soil: Attractive force -Van der

waals force acts between two soil particles; Remains same in magnitude

Repulsive force – Due to the double layer of adsorbed water tending to come into contact with each other; directly related to the size of double layers

If net force is attractive – Structure is Flocculated

If net force is repulsive – Structure is Dispersed

Low Water Content: Repulsive force is

small because double layer is not fully developed; net force is attractive.

Makes difficult for particle to move when compactive effort is applied: Result low dry unit weight

High Water Content: Interparticle repulsive

force increases since double layer expands

Particle easily slide over one another and get packed more easily : Result high dry unit weight

Double layer expansion is complete at Optimum Moisture Content (OMC): Result maximum dry unit weight at this stage

Beyond OMC; water does not add to expansion but replaces the soil grains by water: Result a decrease in dry unit weight

First Decrease in dry unit weight with increase in water content

Reason:Capillary tension in pore water prevents soil particle coming close together (Phenomenon- Bulking of Sand- maximum bulkking occurs at 4-5% water content)

Further increase in water content : Menisci are broken and particles move and adopt to a closer packing

Permeabilty higher when compacted dry of optimum than when compacted wet of optimum

At relatively low stress level clays compacted wet of optimum are more compressible

At relatively high stress level clays compacted dry of optimum are more compressible

Organic content

Maximum dry unit weight Vs. Organic content for all compaction test (Das 2006)

Effect of drying history and organic content on optimum moisture content (Das 2006)

Shallow Compaction: Compaction depends on following factors Thickness of liftArea over which the pressure is appliedIntensity of pressure applied to the soilType of rollerNumber of roller passes

Effect of number of passes on compaction of lean clay

Smooth Wheel RollerProvide a smooth finished gradeUsed for pavingEffective only upto 20-30 cm, [Therefore place the soil in shallow layers (Lifts)]

Greater compaction pressure,Provides kneading action, “walk out” after compactionEffective for compacting fine-grained soil / Clays

Effective for compacting clayey soil and silty soils

Effective for granular soil

Compacted unit weight for 8ft (2.44m) lift height for 2,5,15 and 45 vibratory roller passes

Provides deeper compaction (2-3 m) eg. Air fields

Pounder (Tamper)

Crater created by the impact

(to be backfilled)

Suitable for granular soils, land fills and karst terrain with sink holes.(Solution cavities in lime stone)

Pounder (Tamper)Mass = 5-30 tonneDrop = 10-30 m

Suitable for granular soils

Practiced in several forms:

vibro–compaction

stone columns

vibro-replacement

Vibroflot (vibrating unit)Length = 2 – 3 mDiameter = 0.3 – 0.5 mMass = 2 tonnes(lowered into the ground and vibrated)

vibrator makes a hole in the weak ground

hole backfilled ..and compacted Densely compacted stone column

For densifying granular soils

FireworksAftermath of blasting

Site: Anpara Thermal Power Plant, Uttar PradeshExpansion of existing thermal power plant:Unit D of 2x 500 MW CapacitySite allocated for Expansion: An abandoned Ash Pond of area app. 5400 acres.Depth of Site: 3m to 13mState of Denseness: Loose to Medium dense in conditionExisting bearing capacity of the flyash deposit: < 10 t/m2

Site falls under Zone III – IS 1893 (Part1) 1982- Susceptible to liquefactionMethod adopted for improvement of the Ash Pond: Vibro Stone Column (Dry bottom feed method)

Soil Strata:Ash deposit 3-13mClayey silt/Silty clay upto 23mDense sandy silt or Hard clayey silt with occasionally weathered rock (Granitic gnesis) Density within Ash deposit: Considerable variationSPT value of Ash deposit – Range of N 2 to 30, but on an average 3 to 8SPT value of Hard Clayey Silt : N ranges between 9 and 30

Vibro Stone Column (Bottom feed method):Method does not require water for penetration thus avoiding the disposal of large quantities of muck and also making environmental friendlyRig used: Vibrocat, operational avantage is it is able to exert a pull down force improving penetration speedVibrocat feeds the Coarse granular material to the tip of vibrator with the aid of pressurized airInstallation method consists of alternate step of penetration and retractionDuring retraction gravel runs into the annular space created and then compacted using vibrator thrusts and compressed air

Improving Bearing Capacity of open foundation

Vibro stone column of dia 0.9m at 2m centre to centre spacing in a triangular grid pattern resulted the bearing capacity value 10t/m2

Vibro stone column enhanced the density of Fly ash deposits, which inturn improved Lateral load carrying capacity.

After Improvement, Result Reported:Design lateral load capacity = 7 tUltimate Load = 20 t

Typical detail of stone column installed surrounding the piles

The selection of right depth, right diameter and proper compaction is essential.

Computerised monitoring of penetration depth of vibrator.

Sensor within the depth vibrator indicates the compaction effort of depth vibrator.

General Procedure in Compaction Tests Depending on the size of the compaction mould,

a fraction of the soil sample having particle size larger than a specific value, say d0, is discarded

For example, in the standard Proctor compaction test, the soil particles coarser than 19 mm are discarded before compacting soil in the standard 101.6 mm-diameter laboratory mould; IS270 (Parts 7 and 8) recommends 100-mm diameter mould (BIS, 1980, 1983); AS1289.5.1.1 (Standards Australia, 2003) recommends 105-mm diameter mould

If the fraction removed is significant, the laboratory optimum moisture content and the maximum dry unit weight determined for the remaining soil are not directly comparable with the field values.

To make laboratory values more representative,

the following approaches can be used:

In the laboratory soil sample for conducting the test, the coarse fraction larger than d0, say 19 mm, is replaced by an equal amount of material between 19 mm and the next smaller sieve size, say 4.75 mm;

The water/moisture content and dry unit weight of the discarded coarse fraction (larger than d0) are estimated and the field values are computed as weighted averages of those of the discarded coarse fraction and of the remaining soil.

The field optimum moisture content is calculated using water content of coarse fraction (larger than d0) as described above in second approach, and then the maximum dry unit weight is calculated assuming that the saturation of the soil in field is equal to that achieved in the laboratory test. This treatment is equivalent to shifting the compaction curve upward along a saturation line. It requires knowledge of the specific gravity of the soil particles.

d, max

optimum water content

Zero Air Void CurveSr =100%

First step: To calculate the saturation from the laboratory values of maximum dry unit weight, optimum moisture content and specific gravity of soil particles.

Second step:The equivalent field unit weight is then computed from the laboratory degree of saturation, field optimum moisture content and specific gravity of soil particles.

d, max

optimum water content

Zero Air Void Curve

Sr =100%

Field Compacted Sample Laboratory Compacted Sample

When the coarser fraction, larger than size d0 (e.g. 19 mm), is removed, it also takes away some water associated with its water content. In addition, there is also possibility of some change in the air void volume when the soil is compacted without this coarse fraction.

1/γdF=(1-p)(1+β)/γdL+p/Gcγw+(pWc-(1-p)βWL)/γw-(1-p)β/(Gfγw)

WF = (1-p)WL+pWc

Gf = specific gravity of the fine soil particles (smaller than d0) in the field/laboratory soil sample

Va = volume of the air in voids of the field soil sample VF = total volume of field soil sample VL = total volume of the laboratory soil sample wc = water content of the coarse soil particles in the field soil sample Ws = weight of the soil particles in the field sample Wwc = weight of the water with coarse soil particles in the field soil sample Wwf = weight of the water with fine soil particles in the field/laboratory soil sample α = ratio of volume of the air in voids of the laboratory sample to that in the field soil

sample Gcγw = unit weight of the coarser fraction of soil particles in the field soil sample Gfγw = unit weight of the finer fraction of soil particles in the field/laboratory soil

sample .

The authors wish to acknowledge all the sources (journals/books/photographs) used for the preparation of this presentation.

Thank you.