soil compaction
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Chap. 5: Soil Compaction [()]
5.1 Introduction5.2 General Compaction Principles5.3 Proctor Test5.4 Compaction on Cohesive Soil5.5 Compaction on Cohesionless Soil5.6 Field Compaction5.7 Specifications for Field Compaction5.8 Field Compaction Quality Control5.9 Special Field Compaction Techniques
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What is compaction?Soil compaction is defined as the method of mechanically increasing the density of soil by reducing volume of air through external compactive effort.
5.1 Introduction
Solids
Water
Air
Solids
Water
Air
Compressedsoil
Load
SoilMatrix
soil (1) = WT1VT1 soil (2) = WT1VT2
soil (2) > soil (1)
-
What is compaction?
Compactiveeffort
+ water =
MOISTURE DENSITY RELATIONSHIP
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Purposes of Compactionz Application of energy to soil to reduce the void ratio
- This is usually required for fill materials, and is sometimes used for natural soils
z Reduces compressibility/settlements under working loadsz Reduce the permeability (makes water flow through soil more difficult)z Increases the soil strength z Prevent liquefaction () during earthquakes
5.1 Introduction
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5.2 General Compaction Principles ( )z rollingsmechanical energydensificationcompaction
z 1. 2. 3. 4.5.
-
z 5.1(0) ()(opt)()(optimum moisture content, OMC)optopt(compaction curve)Proctor ()
0d
-
()ProctordW
5.1d
5.2(5.2)d5.2eGsS
5.3 (5.3)
5.4
5.5
VW=
+= 1d
eG ws
d += 1
SGG
s
sd /1
+=
)1(sd
w
GS =
SGe s /=
-
()S=100%S=1 (5.4)zero-air-void unit weight
5.6(5.6)Gs zero-air-void curve5.2Gs(5.6) 5.2 S=60%, S=80S=100% 4Epeakline of optimum
wGwGG
s
w
s
wszav +=+= /11
zav
/
Impossible
zav
zav
d d
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z Factor Affecting Soil Compaction: ()1 - Soil Type being compacted2 - Water Content (wc) of soil3 - The Amount of Compaction Effort (Energy) Used4 Compaction Method Used Soil Type5.3aASTM D698
Impossible
ZAV
-
Water ContentLeeSuedkamp (1972)355.3bA3070B1.5dQPPdB30C3070DdLL>70
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Compaction EffortEJ/m3 (ft-lbf /ft3)1 J ()1 N-m Proctor
(5.7)Wh = impactN
H = mNB = NL = Vm = m3
E5.2E1>E2>E3>E4E 5.2E1>E2>E3>E4dmaxopt
m
BLh
VNNHW
E***=
Increasing compaction energy Lower OMC and higher dry density
Impossible
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Compaction Method impact(kneading)(static)(vibratory)SeedChan (1959)(5.4)
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5.3 Proctor Test Lab. Compaction ()
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5.1 ASTM
3/4 in3/8 in#43/4 in19mm
3/8 in9.5mm
#40.42mm
562525562525NB555333NL
45718
45718
45718
30512
30512
30512
H mmin
44.510
44.510
44.510
24.45.5
24.45.5
24.45.5
W h Nlbf
116.34.58
116.34.58
116.34.58
116.34.58
116.34.58
116.34.58
152.46
101.64
101.64
152.46
101.64
101.64
21241/13.33
9441/30
9441/30
21241/13.33
9441/30
9441/30
CBACBA Vm cm3
ft3
mmin
mmin
270056000
60012400
kN-m/m3ft-lbf/ft3
ASTM D1557-91ASTM D698-91
336
36 591 1091.510944253305.04.24
mmkN
mmN
mmN
VNHNWE
m
LBh ==== ProctorE:
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Soil Compaction in the Lab:1- Standard Proctor Test2- Modified Proctor Test
Standard Proctor Test Modified Proctor Test
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Soil Compaction in the Lab:
1- Standard Proctor Test
wc1 wc2 wc3 wc4 wc5
d1 d2 d3 d4 d5OptimumMoistureContent
WaterContent
Dry Density
d max
Zero Air Void CurveSr =100%
CompactionCurve
1
2
3
4
5
(OMC)
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
eG ws
dry += 1
dry =wet
Wc100
%1+
ZAV =Gs w
WcGs1+Sr
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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
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Example:The laboratory test for a standard proctor is shown below. Determine the optimum water content and maximum dry density. If the Gs of the soil is 2.70, draw the ZAV curve. Solution:
dry =wet
wc100
%1 +
Volume of Proctor Mold
(ft3)
1/301/301/301/301/301/30
Weight of wet soil in the mold
(lb)
3.884.094.234.284.244.19
Water Content Wc (%)
121416182022
Volume of Mold (ft3)
1/301/301/301/301/301/30
Weight of wet soil in the mold
(lb)
3.884.094.234.284.244.19
Water ContentWc(%)
121416182022
Wet Unit Weight(lb/ft3)
116.4122.7126.9128.4127.2125.7
Dry Unit Weight(lb/ft3)
103.9107.6109.4108.8106.0103.0
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
10 11 12 13 14 15 16 17 18 19 20 21 22 23
Gs wwc
ZAV =Gs1 +
Sr
-
E5-2 % g/cm3
8.17 1.74110.21 1.83011.63 1.88614.10 1.88216.32 1.80818.45 1.733
% g/cm38.17 1.74110.21 1.83011.63 1.88614.10 1.88216.32 1.80818.45 1.733
5-2(Proctor)E5-2
O.M.C.
Excel(OMC)
99%[89]
3maxd cm/g885.1)(%73.12.C.M.O ==
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5.4 Compaction on Cohesive Soil ( )(opt)opt(dry of optimum)opt(wet of optimum)opt(near or at optimum)
. (Structure of Compacted Clay Soil )Seed Chan (1959)Lamb(1958)(flocculated)5.5AErandomdispersed5.5CD5.5D
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II. :
1. stiffnessSeedChan19595.6-()ductility
2. (shear strength)5.65.7UU
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3. (permeability)
(a) Lambe19585.810~100Lambe1958
5.7 (SeedChan, 1959))
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(b) compactive effortsMitchell19655.11
(c) compaction methodimpactstatickneading5.12
5.10 k
5.11 k
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z Olson1963clod modelclodsvoidhard clodssoft clods
z Mitchell19655.10
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(d) clodskk310-7cm/sec910-9 cm/sec
(e) Plasticity indexPIPIk
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4. Shrinkage and SwellingSeed and Chan19595.4 5.13
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5.2
10. 9. 8.
7. 6. 5. 4. 3. 2. 1.
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5.5 Compaction on Cohesionless Soil ()()()(proctor)5.3GW
5.3
18-2016-1914-16SP19-2118-2013-16SM
2118-2115-17SW2218-2018GP
21-2318-2117-19GM22-2320-2218-19GW
(kN/m3)Proctor (kN/m3)
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Terzaghi(1925)(Compactibility factor)FF
(5.8) 0.5-2.0F0.5-1.0F1.5-1.8Dr (relative density)(density index) IDDrTerzaghi(1925)(loose0
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Effect of Energy on Soil CompactionIncreasing compaction energy Lower OMC 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 DensityHigherEnergy
ZAV
Water Content
E2
E3
E4 (< E3 < E2 < E1)
E1
5.6 Field Compaction ( )
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Field Compaction Equipment(roller)(vibrating plate)(vibrating rammer)
a. [smooth(steel) wheel (drum) roller]b. (pneumatic rubber-tired roller)c. (sheepsfoot roller )d. (grid roller)e. (vibratory roller)
(lift thickness)
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Soil Compaction equipment in the Field:
1- Rammers()
2- Vibratory Plates( )
3- Smooth-Wheel Rollers ()
4- Pneumatic Rubber-Tired Roller
()
5- Sheepsfoot Roller ()
6- Dynamic Compaction ()
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Field Compaction Equipment
Compacts effectively only to 200-300 mm; therefore, place the soil in shallow layers (lifts)
Smooth Wheeled Roller
100%380kPa(proof rolling subgrade)10-15()
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Field Compaction Equipment
for compacting very small areas effective for granular soils
Vibrating Plates
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Pneumatic rubber tired rollerField Compaction Equipment
4680%700kPa50Ton45()
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Provides kneading action; walks out after compaction
Very effective on clays
Sheepsfoot RollerField Compaction Equipment
25-80cm28%-12%1400kPa-7000kPa15-30cm
-
Provides deeper (2-3m) compaction. e.g., air field
Impact Roller
Field Compaction Equipment
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Field Compaction Equipment
(grid roller)50%1400kPa-6200kPa
(vibratory roller)1 m
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z
1. 4.14
Factors Affecting Field Compaction
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2. (no. of passes)5.15()5.164-84-815-20
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3. (thickness of lift)(1)(2)5.14(3)5.17A(4)A()50-100kPa(400-700kPa)
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5.7 Specifications for Field Compaction
1.
2. 3. 4. 5.
(1)(end-product specification) (2)(method specification)
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5.7 Specifications for Field Compaction
Compaction performance parameters are given on a construction project in one of two ways:
1- Method Specification (( ))Detailed instructions specify machine type, lift depths,
number of passes, machine speed and moisture content. A "recipe" is given as part of the job specifications to accomplish the compaction needed.
2- End-Product Specification ()Only final compaction requirements are specified (95%
modified or standard Proctor). This method, gives the contractor much more flexibility in determining the best, most economical method of meeting the required specs.
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z (relative compaction)(percent compaction)
z Rc(dry density ratio) ProctorProctor
(5.9)(granular soil)
(5.10)z Ro =d,min/d,max(5.10)
(5.11)z LeeSingh(1975)47
Rc = 80 + 0.2Dr (5.12)
fd,ld max,, 100(%)
max,,
, =ld
fdcR
100(%)max,,
, =ld
fdc r
rR
100)((%),
max,
min,max,
max,, =
fd
d
dd
dfdrD
)1(1(%)
or
oc RD
RR =
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z (criteria)
z A(95%()Proctor)5.18 (Seed,1964)5.18EA > EB> EC90%EAadadEA90%cECEC(EB)optc
5.18 (Seed,1964)
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z(overcompaction)zBProctorProctorzCProctorProctor
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5.8 Field Compaction Quality Control- a systematic exercise where you check at regular intervals whether the compaction was done to specifications.
e.g., 1 test per 1000 m3 of
compacted soil
Minimum dry density Range of water content
Field measurements (of d) obtained using sand cone
nuclear density meter
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Laboratory Compaction Test- to obtain the compaction curve and define the optimum water content and maximum dry density for a specific compactive effort.
hammerStandard Proctor Test: Modified Proctor Test:
3 layers
25 blows per layer
2.7 kg hammer
300 mm drop
5 layers
25 blows per layer
4.9 kg hamer
450mm drop
1000 ml compaction mould
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Compaction Quality Control Test
compacted ground
d,field = ?field, V= ?
Compaction specifications
Compare!
wc
d
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Field Soil CompactionBecause of the differences between lab and field compaction methods, the maximum dry density in the field may reach 90% to 95%.
MoistureContent
Dry Density
d max
(OMC)
ZAV
95% d max
Field measurements (of d) obtained usingz sand conez rubber balloonz nuclear density meter
-
Determination of Field Unit Weight of Compaction
Three methods are used:
1 - Sand Cone Method (ASTM D1556-90) 2 - Rubber Balloon Method3 - Nuclear Density Method (ASTM D2292-91)
1 - Sand Cone Method (ASTM D1556-90) ()A small hole (6" x 6" deep) is dug in the compacted material to be tested. The soil is removed and weighed, then dried and weighed again to determine its moisture content. A soil's moisture is figured as a percentage. The specific volume of the hole is determined by filling it with calibrated dry sand from a jar and cone device. The dry weight of the soil removed is divided by the volume of sand needed to fill the hole. This gives us the density of the compacted soil in lbs per cubic foot. This density is compared to the maximum Proctor density obtained earlier, which gives us the relative density of the soil that was just compacted.
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1. W
2. Ws = W/(1 + )
3. ()5.19:()d,s5.19(a)WTWc ()W2 = WT Ws - WcVV = W2 / ds
4. V
(5.13)5. Rc
(5.14)
VWs
fd =,
%100max,
, =d
fdcR
5.19 (a)
d,maxProctorProctor
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2 - Rubber Balloon Method
The same as the sand cone, except a rubber balloon is used to determine the volume of the hole.5.19(b)V(ASTM D2167-84 )
5.19(b)
()
-
3 - Nuclear Density Meter Method (ASTM D2292-91) ()
Nuclear Density meters are a quick and fairly accurate way of determining density and moisture content. The meter uses a radioactive isotope source (Cesium 137) at the soil surface (backscatter) or from a probe placed into the soil (direct transmission). The isotope source gives off photons (usually Gamma rays) which radiate back to the mater's detectors on the bottom of the unit. Dense soil absorbs more radiation than loose soil and the readings reflect overall density. Water content (ASTM D3017) can also be read, all within a few minutes.
-
z(nuclear density meter method)(cesium 137)(Gamma)(Geiger-Muller Counter)-(backscatter mode)(direct transmission mode)4.20z-(americium 241beryllium)-3(helium-3 detection tube )
3 - Nuclear Density Meter Method
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5.9 Special Field Compaction TechniquesI. (preloading or precompression method)(surcharge)II. (heavy tamping)(dynamic compaction)(dynamic consolidation) (10~40ton)1040m()
-
1930(depth of influence), dim
di = n (4.14)
W(Ton)h(m)n0.3 ~ 1.0nn0.5 ~ 1.0n0.3 ~ 0.5Leonards, CutterHoltz (1980)n = 0.5
[] 20Ton15mdi =
[] n = 0.5 di = 0.5 = 8.66m
Wh
20 15
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II. Dynamic Compaction- pounding the ground by a heavy weight
Suitable for granular soils, land fills and karst terrain with sink holes.
Crater created by the impact
Pounder (Tamper)solution cavities in limestone
(to be backfilled)
-
II. Dynamic Compaction
Pounder (Tamper)Mass = 5-30 tonneDrop = 10-30 m
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II. Dynamic Compaction
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III. (vibroflotation)z 19300.3 ~ 0.5m3 ~ 8m(vibrator) 30 ~ 50Hz220KN25mm0.8MPa3m3/
-
1. 1 ~3m/
2. 3. 30cm/4. 10m0.27 ~ 1.8m3
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II. Dynamic Compaction
-
1.5 ~ 3m2 ~ 2.5m
(a) 5.22123
(b) Brown (1977)(suitability number)SnSn
Sn = 1.7 (4.15)
D10, D20, D50mmSnSn
Sn 0-10 (excellent)10~20 (good)20~30 (fair)30~50 (poor)>50 (unsuitable
3 1 1
502
202
102D D D
+ +
-
5.22
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III. Vibroflotation
Vibroflot (vibrating unit)Length = 2 3 mDiameter = 0.3 0.5 mMass = 2 tonnes
Practiced in several forms:
vibrocompaction stone columns vibro-replacement
Suitable for granular soils
(lowered into the ground and vibrated)
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III. Vibroflotation
-
Stone Columns ()
vibrator makes a hole in the weak ground
hole backfilled ..and compacted Densely compacted stone column
-
1.5 ~ 3m2 ~ 2.5m
(a) 5.22123
(b) Brown (1977)(suitability number)SnSn
Sn = 1.7 (5.15)
D10, D20, D50mmSnSn
Sn 0-10 10~20 20~30 30~50 >50
3 1 1
502
202
102D D D
+ +
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IV. Blasting
Aftermath of blastingFireworks?
For densifying granular soils
IV. (blasting)(shock wave),?
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Appendix: Earthmoving Equipment
Large Excavator (see minivan on left for scale)
Van
Grader for spreading soil
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Earthmoving Equipment
Bulldozer for spreading soil evenly
Loader
BackhoeCrawler mountedHydraulic Excavator
-
Earthmoving Equipment
Rock Breaker
End of Chapter 5
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