Topic #4

Soil Compaction

What is Compaction?

A simple ground improvement technique, where the

soil is densified through external compactive effort.

+ Water =

Compactive

Effort

2

Phase diagrams showing the changes in soil as it moves from its

natural location to a compacted fill.

Note that the volume of solids does not change during the process.

3

Compaction and Phase Diagram

Changes in volume as soil is excavated, transported, and

compacted. The numerical values are examples and would be

different for each soil.

4

Volumetric Change During Excavation and Compaction

Soil compaction is defined as the method of mechanically

increasing the density of soil by reducing volume of air.

Solids

Water

Air

Solids

Water

Air

Compressed

soil

Load

Soil

Matrix

gsoil (1) = WT1

VT1

gsoil (2) = WT1

VT2

gsoil (2) > gsoil (1)

Definition

5

Compaction of Soils in the Laboratory

6

Compaction in the Laboratory

Compaction test is performed on graded aggregate soils in the

laboratory to obtain the compaction curve. The compaction curve is

used to determine the optimum water content (wopt) and the maximum

dry density (gdry) of the soil sample for a specific compactive effort.

Standard Proctor Modified Proctor

3 layers

25 blows per layer

5 layers

25 blows per layer

2.49 kg (5.5 lb.) hammer

305 mm (12 in.) drop

4.54 kg (10 lb.) hammer

457 mm (18 in.) drop

7

In the standard test we compact the soil in

three layers, (as shown), while in the modified

test we compact the soil in five layers.

Mold and Hammer for a Proctor Compaction Test

8

Compaction Curve

Water content (w%)

Dry

Den

sity

(g d

)

Optimum Moisture

Content (OMC)

- Soil grains densely packed

- Good strength and stiffness

- Low permeabilitygd (max)

9

The water content-density relationship indicating the increased density resulting from the addition of water and

applied compaction effort.

Soil is a silty clay, LL = 37, PI = 14, standard Proctor compaction (after Johnson and Sallberg, 1960).

Beyond OMC,

excess water results

in lower density.

Water acts as a

lubricating agent

and replaces the

air in the void

structure,

therefore results

in higher density

Dry Side:

10

Role of the Water at the Two Sides of the MD Curve

Soil Compaction in the Laboratory

Standard Proctor Test

wc1 wc2 wc3wc4 wc5

gd1 gd2 gd3gd4 gd5

Optimum

Moisture

Content

Water

Content

Dry Density

gd max

Zero Air Void Curve

Sr =100%

Compaction

Curve

1

2

3

4

5

OMC

4 inch diameter compaction mold

(V = 1/30 cubic foot)

5.5 pound hammer

25 blows

per layer

H = 12 in

Wet to

OptimumDry to

Optimum

Increasing Water Content

S

wG

G

s

wsZAV

1

gg

w

wetdry

1

gg

e

G wsdry

1

gg

12

Zero Air Void (ZAV) Curve

All compaction points should

lie to the left of ZAV curve

corresponds to 100% saturation

Water Content (w)

Dry

Density (

d)

Zero air void curve (S=100%)

s

wsd

wG

G

1

S<100%

S>100% (impossible)

13

Methods:

1- Standard Proctor Test

2- Modified Proctor Test

Standard Proctor Test Modified Proctor TestModified Proctor Test

Compaction Energy:12,400 ft.- Ib/ft3

Compaction Energy:56,200 ft.- Ib/ft3

Summary of Proctor Compaction Test

Comparison between Standard and Modified Proctor

Compaction Tests

15

Effect of Compaction Energy

on Moisture-Density Curve

Increasing compactive

effort results in:

E1

E2 (>E1)Lower optimum

water content

Higher maximum dry density

Water content

Dry

den

sity

(

d)

16

Compaction Energy Proctor Tests

1- Standard Proctor Test

ASTM D-698 or AASHTO T-99

2- Modified Proctor Test

ASTM 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 =

Moisture

Content

Dry Density

gd max

Compaction Curve for

Standard Proctor test

gd max

Zero Air Void (ZAV) Curve

Sr = 100%

Line of optimum (LOO)

wp ws

Compaction Curve for

Modified Proctor test

17

Water Content

Dry

Den

sit

y

Effect of Energy on Soil Compaction

Higher

Energy

Increasing compaction energy Lower OMC and higher dry density

In the field increasing compaction

energy = increasing number of

passes or reducing the thickness

of the lift.In the lab increasing

compaction energy =

increasing number of

blows (assuming weight

of the hammer and the

drop height stays the

same) or by dividing the

soil in thinner lifts.

18

Comparison of Standard Proctor Test and

Modified Proctor Test Results for the Same Soil

19

20

Compaction and Clay Fabric

Higher water content

or higher compactive

effort results in more

oriented fabric.

more dispersed fabric

more

dis

pers

ed f

abric

Dry

density (

d)

Moisture Content

Dry

Density

21

Standard and Modified Proctor Compaction Curves

(Summary)

w

wetdry

1

gg

S

wG

G

s

wsZAV

1

gg

22

Improvements in Particle Contacts by

Mechanical Compaction

23

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.

Volume of

Proctor Mold

(ft3)

Weight of Wet Soil

(lb.)

Water Content

(%)

1/30 3.88 12

1/30 4.09 14

1/30 4.23 16

1/30 4.28 18

1/30 4.24 20

1/30 4.19 22

Laboratory Compaction Test

Example

24

Volume of

Proctor Mold

(ft3)

Weight of Wet

Soil

(lb.)

Wet Unit

Weight

(lb/ft3)

Water Content

(%)

Dry Unit

Weight

(lb/ft3)

1/30 3.88 116.4 12 103.9

1/30 4.09 122.7 14 107.6

1/30 4.23 126.9 16 109.4

1/30 4.28 128.4 18 108.8

1/30 4.24 127.2 20 106.0

1/30 4.19 125.7 22 103.0

Laboratory Compaction Test

Solution

w

wetdry

1

gg

mold

wetwet

V

Wg

25

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

gdry max

Optimum Water Content (%)

Dry

De

ns

ity (

lb/f

t3)

S

wG

G

s

wsZAV

1

gg

w

wetdry

1

gg

26

Typical Compaction Specifications

100)(

)(

Labd

FielddRC

g

gRelative Compaction (RC) in percent:

27

Field Compaction Curvess

Because of the differences between lab and field

compaction methods, the maximum dry density in

the field may reach 90% to 95%.

The most efficient

or economical water

content is between

wopt and b.

28

minmax

max

ee

eeDr

(min)(max)

(min)

dd

dd

dIgg

gg

Relative Density or Index Density based on Void Ratio (e)

Relative Density or Index Density based on Dry Density (gd)

Relative Density-Definitions

In practice, its often useful to know how dense or how loose the

soil is with respect to its densest and loosest conditions. That’s

when we use the relative density concept.

e max : Void ratio of the soil in its loosest condition

e min : Void ratio of the soil in its densest condition

e : Current void ratio of the soil in the field

gd (max) : Dry unit weight of the soil in its densest condition

gd (min) : Dry unit weight of the soil in its loosest condition

gd : Current unit weight of the soil in the field

29

Filed Compaction

- Pneumatic rubber tired roller

Different types of rollers (clockwise from top right):

- Vibratory plate

• - Smooth-wheel roller

- Sheepsfoot roller

30

Field Compaction

Compacts effectively only to 200-300 mm;

therefore, place the soil in shallow layers (lifts)

Smooth Wheeled Roller

31

Field Compaction

Commonly used for compacting

relatively small areas, effective for

granular soils.

Vibrating Plates

32

Field Compaction

Provides kneading action;

“walks out” after compaction,

very effective on clays.

Sheepsfoot Roller

33

Field Compaction

Provides deeper (2-3 m) compaction. e.g., airfield

Impact Roller

34

Recent Modifications to the Impact Rollers

36

Grid Roller

Soil types best suited for various kinds of compaction equipment.

(Adapted from Caterpillar, 1993.)

37

Selection of Rollers Based on Soil Type

Compaction Control

A quality control measure where you check

at regular intervals whether the compaction

was done according to specifications.

e.g. one core per 1000 m2 of

compacted soil in the field

Minimum dry density

Range of water content

Field measurements of d obtained using:

Non-Destructive Testing, such as Nuclear Density Gauge

Destructive Testing, such as Sand Cone Test

38

Sand Cone Test

39

Determination of the Soil Density in the Field

Sand Cone Test

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. 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 lb. per cubic foot. This density

is compared to the maximum Proctor density

obtained in the lab, which gives us the relative

density of the compacted soil in the field.

1- Sand Cone (ASTM D1556)

40

Performing Sand Cone Test in the Field

41

Performing a Nuclear Density Test in the Field

42

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.

2- Nuclear Density (ASTM D2292)

43

Determination of the Soil Density in the Field

Nuclear Density Gauge

Nuclear Density meters are a quick 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 detectors at the bottom of the unit.

Intelligent Compaction

Intelligent Compaction (IC) measures stiffness (the ability of

a material to resist deformation under a load) rather than

density of the compacted soil. A strong correlation exists

between stiffness and bearing capacity of foundations.

A machine equipped with an intelligent compaction system

provides four basic functions:

1) Measures the stiffness of the soil.

2) Controls or guides the compaction effort in response to the

measured stiffness.

3) Displays the stiffness measurement to the operator.

4) Maps and records the compaction results.

Such a system would enable the user to produce detailed

plots of the soil stiffness levels, the number of roller passes,

as well as the location and time of the application.

44

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)

45

Dynamic (or Impact) Compaction

46

Dynamic Compaction

Pounder

(Tamper)

Mass = 5-30 ton

Drop = 10-30 m

𝐷 = 𝑛 (𝑊 × 𝐻)0.5

D: Influence depth (improvement)in meters

W: Mass of tamper in mega grams

H: Drop height in meters

n: model parameter, typically less than 1

47

Construction Equipment

Large Dump Truck

48

Grader for spreading soil

49

Construction Equipment

Bulldozer for evenly spreading soil

50

Construction Equipment

Loader

51

Construction Equipment

Backhoe

52

Construction Equipment

Crawler mounted Hydraulic Excavator

53

Construction Equipment

Rock Breaker

54

Construction Equipment

Water Truck

55

Construction Equipment