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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.