soil compaction

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

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

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

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

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

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

Compaction Method impact(kneading)(static)(vibratory)SeedChan (1959)(5.4)

5.3 Proctor Test Lab. Compaction ()

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:

Soil Compaction in the Lab:1- Standard Proctor Test2- Modified Proctor Test

Standard Proctor Test Modified Proctor Test

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

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

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 ==

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

II. :

1. stiffnessSeedChan19595.6-()ductility

2. (shear strength)5.65.7UU

3. (permeability)

(a) Lambe19585.810~100Lambe1958

5.7 (SeedChan, 1959))

(b) compactive effortsMitchell19655.11

(c) compaction methodimpactstatickneading5.12

5.10 k

5.11 k

z Olson1963clod modelclodsvoidhard clodssoft clods

z Mitchell19655.10

(d) clodskk310-7cm/sec910-9 cm/sec

(e) Plasticity indexPIPIk

4. Shrinkage and SwellingSeed and Chan19595.4 5.13

5.2

10. 9. 8.

7. 6. 5. 4. 3. 2. 1.

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)

Terzaghi(1925)(Compactibility factor)FF

(5.8) 0.5-2.0F0.5-1.0F1.5-1.8Dr (relative density)(density index) IDDrTerzaghi(1925)(loose0

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 ( )

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)

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 ()

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()


for compacting very small areas effective for granular soils

Vibrating Plates

Pneumatic rubber tired rollerField Compaction Equipment

4680%700kPa50Ton45()

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



(grid roller)50%1400kPa-6200kPa

(vibratory roller)1 m

z

1. 4.14

Factors Affecting Field Compaction

2. (no. of passes)5.15()5.164-84-815-20

3. (thickness of lift)(1)(2)5.14(3)5.17A(4)A()50-100kPa(400-700kPa)

5.7 Specifications for Field Compaction

1.

2. 3. 4. 5.

(1)(end-product specification) (2)(method specification)

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.

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 =

z (criteria)

z A(95%()Proctor)5.18 (Seed,1964)5.18EA > EB> EC90%EAadadEA90%cECEC(EB)optc

5.18 (Seed,1964)

z(overcompaction)zBProctorProctorzCProctorProctor

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

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

Compaction Quality Control Test

compacted ground

d,field = ?field, V= ?

Compaction specifications

Compare!

wc

d

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.

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

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

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

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

III. (vibroflotation)z 19300.3 ~ 0.5m3 ~ 8m(vibrator) 30 ~ 50Hz220KN25mm0.8MPa3m3/

1. 1 ~3m/

2. 3. 30cm/4. 10m0.27 ~ 1.8m3

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

+ +

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)

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

+ +

IV. Blasting

Aftermath of blastingFireworks?

For densifying granular soils

IV. (blasting)(shock wave),?

Appendix: Earthmoving Equipment

Large Excavator (see minivan on left for scale)

Van

Grader for spreading soil

Earthmoving Equipment

Bulldozer for spreading soil evenly

Loader

BackhoeCrawler mountedHydraulic Excavator

Earthmoving Equipment

Rock Breaker

End of Chapter 5

soil compaction

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