References

Das, B., M. (2014), “ Principles of

geotechnical Engineering ” Eighth
Edition, CENGAGE Learning,
ISBN-13: 978-0-495-41130-7.
Knappett, J. A. and Craig R. F. (2012), “
Craig’s Soil Mechanics” Eighth Edition,
Spon Press, ISBN:
978- 0-415-56125-9.

1
 Introduction
In the construction of highway
embankments, earth dams, and
many other engineering structures,
loose soils must be compacted to
increase their unit weights. To
compact a soil, that is, to place it in a
dense state. The dense state is
achieved through the reduction of
the air voids in the soil, with little or no
reduction in the water content. This
process must not be confused with 2

consolidation, in which water is

 Compaction of Soil
Compaction increases the strength
characteristics of soils, which
increase the bearing capacity of
foundations constructed over them.
Compaction also decreases the
amount of undesirable settlement of
structures and
increases the stability of slopes of
embankments.

3
 Compaction of Soil

Poor Good Poor Good Poor Good

compaction compaction compaction compaction compaction compaction

Increased bearing Higher resistance Increased stability

capacity to deformation Decreased permeability
Increased Higher resistance
durability to frost damage

4
 Purposes of
compacting
1) Increased Shear soil
Strength
This means that larger loads can
be applied to compacted soils
since they are
typically stronger. Increased
Shear Strength => increased
bearing capacity, slope stability,
and pavement system strength
2) Reduced Permeability
This inhibits soils’ ability to
absorb water, and therefore
reduces the tendency to 5

expand/shrink and potentially

 Purposes of
compacting soil
3) Reduced Compressibility
This also means that larger
loads can be applied to
compacted soils since
they will produce smaller
settlements.
4) Control Swelling & Shrinking
5) Reduce Liquefaction
Potential
6
 Compaction of Soil
Definition:

Compaction, in general, is the

densification of soil by removal of
air, which requires
mechanical energy. Simplistically,
compaction may be defined as
the process in which soil particles
are forced closer together with
the resultant reduction in air
voids.
7
 Principles of Compaction

Compaction of soils is achieved by

reducing the volume of voids. It is
assumed that the compaction
process does not decrease the
volume of the solids or soil grains·

Soil compact Soil compa

before ed before cted
compact compact 8
ion ion
 Principles of Compaction

Compaction
Effect
Air Air

Water Water

Solids Solids

Loose Compacte
soil d soil

9
 Principles of Compaction

The degree of compaction of

a soil is measured by
the dry unit weight of the
skeleton.

yd = yw
The dry unit weight correlates
with the degree1ofpacking
+
Gse
of the
soil grains.
The more compacted a soil is:
• the smaller its void ratio (e) will
be.
• the higher its dry unit weight 10

( y ) will be
 Compaction Curve

The compaction curve is

relationship between a soil water
content and dry unit weight.
Soil sample was computed at

of volume 1000ycc and dry unit

different water contents in a cylinder
ydobtained.
1+
=
weight were
we
Compaction curve is plotted between
the water content as abscissa and
the dry density as ordinate.
11
 Compaction Curve

It is observed that the dry density

increases with an increase in water
content till the max. density is
attained. With Further increase in
water content, the dry density
decreases.
20
weight(γd)
Dry unit

18

16
12
Water Content
8 10 12 14 16 18 (Wc)
20 22
14 12
 Compaction Curve
Optimum moisture content (OMC) :
The water content corresponding to
maximum dry unit weight is called
optimum moisture content.
Note that the maximum dry unit weight is only
a maximum for a specific compactive effort and
method
18
of compaction.
y dmax
weight(γd)

16
Dry unit

14

12
OM Water Content
8 10 12C 14 16 18 (Wc)
20 22
13
 Compaction Curve
Optimum moisture content (OMC) :
Each compactive effort for a given soil has
its own OMC. As the compactive effort is
increased, the maximum density generally
increases and the OMC decreases.
y dmax1

18
y dmax2
weight(γd)
Dry unit

16

14
12
OMC OMC Water Content
8 101 12 142 16 18 (Wc)
20 22
14
 Compaction Curve

Zero air voids curve or saturation line

The curve represent the fully saturated
condition ( S= 100%). ( It can not be
yw Gs
yd
1 + we ∗
reached byunit
Theoretical compaction
weight is)
=
Gs
given as
y dma
x
18 "Zero Air
Voids" S =
weight(γd)

16
100%
Dry unit

14

12
OM Water Content
8 10 12C 14 16 18 (Wc)
20 22
15
 Compaction Curve

Line of Optimums
A line drawn through the peak points of
several compaction curves at
different compactive efforts for the same
soil will be almost parallel to a zero air
voids curve , it is called the line of
optimums
18 "Zero Air
Line of Optimums
Voids" S =
weight(γd)

16
100%
Dry unit

14

12
Water Content
8 10 12 14 16 18 (Wc)
20 22
16
 Factors affecting
Compaction
• Water content of the soil
• Amount ofcompaction
• Type of soil being compacted
• The amount of
compactive energy used
• Method of compaction
• Thickness of layer
• Saturation line
• Admixtures
• Stone content
17
 Factors affecting
Compaction
Water content of the soil
As water is added to a soil ( at low
moisture content) it acts as a softening
agent on the soil particles
andbecomes easier for the particles to
move past one another during the
application of the
compacting forces. As the soil
compacts the voids are reduced and
this causes the dry unit weight ( or dry
density) to increase. 18
 Factors affecting
Compaction
Water content below OMC
As the water content increases, the
particles develop larger and larger water
films around them, which tend to
“lubricate” the particles and make them
easier to be moved about and reoriented
20
into a denser configuration.
18
weight(γd)

16
Dry unit

14

12
OM Water Content
8 10 12C 14 16 18 (Wc)
20 22
19
 Factors affecting
Compaction
Water content at OMC
The density is at the
maximum, and it does not
increase any further.
20

18
weight(γd)

16
Dry unit

14

12
OM Water Content
8 10 12C 14 16 18 (Wc)
20 22
20
 Factors affecting
Compaction
Water content above OMC
Water starts to replace soil
particles in the mold and the
dry unit weight starts to
decrease.
20
weight(γd)

18
Dry unit

16

14
12
OM Water Content
8 10 12C 14 16 18 (Wc)
20 22
21
 Factors affecting
Compaction
Soil type
Soil type, grain size, shape of
the soil grains, amount and type of
clay minerals present and the
specific gravity of the soil
solids, have a great influence on the
dry unit weight and optimum
moisture content
Uniformly graded sand or poorly
graded in nature is difficult to
compact them. 22
 Factors affecting
Compaction
Soil type
In poorly graded sands the dry unit
weight initially decreases as the
moisture content increases and then
increases to a maximum value with
further increase in moisture content.
At lower moisture content, the
capillary tension inhibits the
tendency of the soil particles to
move around and be compacted.
23
 Factors affecting
Compaction
Soil type
At a given moisture content, a
clay with low plasticity will be
weaker than a heavy or high
plastic clay so it will be easier to
compact.

24
 Factors affecting
Compaction
Structure of
Compacted Clay
Intermed
iate
structur High
e Compact Dispersed
ive Effort Structure or
parallel
Low Compactive Effort
Dry Unit
Weight

Flocculated
Structure, or
Honeycomb
Structure, or Water
Random Content
25
 Factors affecting
Compaction
Effect of Compaction effort
The compaction energy per unit
volume used for the standard
No. o f No. weigℎt ℎeigℎt
Proctor test can be given as
× × ×
blows of of of
E
per layer laye
Volume o ℎamme
f drops
=
rmold r

26
 Factors affecting
Compaction
Effects of increasing compactive
effort
Increased compactive effort enables
greater dry unit weight. It can be seen
from this figure that the compaction
curve is not a unique soil
characteristic.
18 High compactive
It depends on the
y dmax effort curve
weight(γd)

16 2
compaction energy. Low compactive
Dry unit

14
y dmax1 effort curve
12
OMC OMC Water Content
8 1 2 18 (Wc)
27
10 12 20 22
14 16
 Factors affecting
Compaction
Effects of increasing compactive
effort
For this reason it is important when
giving values of (γdry)max and OMC to
also specify the compaction procedure
(for example, standard or modified).
From the preceding observation we can
see that
1.As the compaction effort is increased, the
maximum dry unit weight of compaction
is also increased.
2.As the compaction effort is 28
increased, the optimum moisture
content is decreased to some extent.
 General Compaction
Methods
Coarse-grained soils Fine-grained
soils
Falling weight and
Laborat

Vibrating hammers Kneading

hammer
ory

compactors
Vibratio Static Kneadi
loading and
press
n
 Hand-operated ng
 Hand-operated
vibration plates tampers
Fiel

 Motorized vibratory  Sheep-foot

d

rollers  Rubber-tired
rollers
 Rubber-tired equipment rollers
 Free – falling
weight dynamic 29

compaction
 Laboratory Compaction
Tests
Laboratory compaction tests
provide the basis for determining
the percent compaction and
molding water content needed to
achieve the required engineering
properties, and for controlling
construction to assure that the
required compaction and water
contents are achieved.

30
 Laboratory Compaction
Tests
The aim of the test is to establish
the maximum dry unit weight that
may be attained for a given soil with
a standard amount of compactive
effort.
When a series of samples
of a soil are
compacted at different water
content the plot usually shows a
distinct peak.
31
 Laboratory Compaction
Tests
The fundamentals of
compaction of fine- grained
soils are relatively new. R.R.
Proctor in the early 1930’s
developed the principles of
compaction.
The proctor test is an impact
compaction. A hammer is dropped
several times on a soil sample in a
mold. The mass ofthe hammer,
height of drop, number of drops, 32

number of layers of soil, and

 Laboratory Compaction
Tests

There are several types of

test which can be used to study the
compactive properties of
soils.
1. Standard Procter Test is not
sufficient for airway and
highways,
2.Modified Procter Test was later
adopted by AASHTO and ASTM 33
 Standard Procter Test

Soil is compacted into a mould in 3-5

equal layers, each layer receiving 25
blows of a
hammer of
standard weight. The energy
(compactive effort) supplied in this
Volume of Hammer mass Drop of
testmould
is 595 kJ/m . The important
3
hammer
dimensions
1000 cm3 are 2.5 kg 300 mm

34
 Standard Procter Test
Standard Proctor test
equipment

35
 Standard Procter Test
Standard Proctor test
equipment

36
 Standard Procter Test

Proctor established that compaction

is a function of four variables:
• Dry density (d) or dry unit weight
d.
• Water content wc
• Compactive effort (energy E)
• Soil type (gradation, presence of
clay minerals, etc.)
37
 Standard Procter Test

The soil is mixed with varying

amounts
of water to achieve different
water contents
Several samples of the same
soil , but at different water
contents, are compacted
according to the compaction
test specification 38
 Standard Procter Test

Apply 25 blows from the rammer

•

dropped from a height of 305 mm

above the soil.

39
 Standard Procter Test

Distribute the blows uniformly over

•

the surface and ensure that the

rammer always falls freely
4
and is not
5
obstructed.4 6

1 2 7
etc.
3 8

The first four blows The successive

blows
Rammer Pattern for compaction in
101.6 mm Mold 40
 Standard Procter Test
The soil is in mold will be divided
into three lifts
Each Lift is compacted 25 2.5 kg
(5.5lb)
times 25 blows
per layer
• Place a second quantity
of moist soil in the

mm
305
mould such that when
compacted it occupies
a little over two-thirds
of the height of
the mould body.
41

Soil
sample
 Standard Procter Test

Repeat procedure once

•

more so that the 2.5 kg

(5.5lb)
amount of soil used is 25 blows
sufficient to fill the per layer

mould body, with the

surface not more than

mm
305
6mm proud of the
upper edge of the
mould body. Soil
sample
3 layers
42
 Standard Procter Test

The unit weight and the actual

water content of each compacted
sample are measured
Derive the dry unit weight from the
known unit weight 𝛾and water
content𝛾 𝑑=
1 +𝑤

43
 Standard Procter Test

Plot the dry unit weight versus

water content for each compacted
sample.
Determine the maximum dry weight
and18OMC "Zero Air
Voids" S =
y dmax
weight(γd)

16 100%
Dry unit

14

12
OMC
8 10 20 22
12 14 16
18

Water Content 44
(Wc)
 Standard Procter Test
Specification of standard Proctor test ( Based
on ASTM Test Designation 698)
Ite Method A Method B
m
Diameter of mold 101.6 mm
Method C 101.6 mm 152.4
mm
Volume of mold 943.3 cm3 943.3 cm3 2124
cm3
Weight 24.4 N 24.4 N 24.4 N
of hammer Height
304.8 mm 304.8 mm 304.8
of hammer drop mm
Number of hammer
blows per layer 25 25 56
of soil

Number of
layers of 3 3 345
compaction
591.3 591.3 591.3
 Standard Procter Test
Specification of standard Proctor test ( Based
on ASTM Test Designation 698) ( con.)
Ite Method A Method B
m Method Portion Portion
Soil to be used Portion C
passing passing passing 19-
No.4 9.5 mm sieve .
( 4.75mm)s mm May be used
ieve. May sieve if more than
be used if . 20% by
20% or less May be used weight of
by if retained on material is
weight No.4 sieve is retained on
of the more than 9.5 mm
material 20% and sieve and
is 20% or less less than
retained by weight of 30% by
on material is weight of
No.4 retained on material is
sieve. 9.5 retained on
mm sieve. 19- mm 46
sieve.
 Modified Procter Test

• Was developed during World

War II
• By the U.S. Army Corps of
Engineering
• For a better representation of
the compaction required for
airfield to support heavy
aircraft.

47
 Modified Procter Test

Same as the Standard Proctor

Test with the following
exceptions:
 The soil is compacted in five
layers
 Hammer weight is 10 Lbs or
4.54 Kg
 Drop height h is 18 inches or
45.72cm
 Then the amount ofEnergy is 48

calculated
 Modified Procter Test
Uniformly distribution
of 44.5 N(10
the blows over the lb)

surface 4
6 9

457.2
1 5 2

mm
8 7 # 5

3 # 4

# 3

Rammer Pattern for # 2

compaction in # 1

152,4 mm Mold
49
 Modified Procter Test
Specification of standard Proctor test ( Based
on ASTM Test Designation 698)
Ite Method A Method B
m
Diameter of mold 101.6 mm
Method C 101.6 mm 152.4
mm
Volume of mold 943.3 cm3 943.3 cm3 2124
cm3
Weight 44.5 N 44.5 N 44.5 N
of hammer Height
457.2 mm 457.2 mm 457.2
of hammer drop mm
Number of hammer
blows per layer 25 25 56
of soil

Number of
layers of 5 5 550
compaction
2696 2696 2696
 Modified Procter Test
Specification of standard Proctor test ( Based
on ASTM Test Designation 698) ( con.)
Ite Method A Method B
m
Soil to be used Portion passing
Method C Portion Portion
No.4 passing passing 19-
(457mm)sieve 9.5 mm mm sieve .
May be used if sieve . May May be used
be used if if more than
25% or less by soil 20% by
weight of retained on weight of
material is No.4 sieve material is
retained on is more retained on
No.4 sieve. than 25% 9.5 mm
If this and 25% or sieve and
gradation less by less than
requirement weight of 30% by
cannot be met, material is weight of
then Methods B retained on material is
or C may be 9.5 retained on
used. mm sieve. 19- mm 51
sieve.
 Comparison-Curves

y dmax
(mod.)
Modified
Dry unit weight

Procter
Test
y dmax
(Stand.)
(γd)

Standard
Procter
Test

OMC
52
Water Content (wc)
 Comparison-Summary

Standard Proctor Test Modified

Proctor Test
 Mold size:  Mold size:
943.3cm^3 943.3cm^3
 304.8 mm height  457.2 mm height
of of
drop drop
 24.4 N hammer  44.5 N hammer
 3 layers  5 layers
 25 blows/layer  25 blows/layer
 Energy 591.3  Energy 2696 53

kN.m/m^3 kN.m/m^3
 Filed Compaction

Compaction Equipment
Most of the compaction in the
field is done with rollers. The
four most common types of
rollers are:
1.Smooth-wheel rollers (or
smooth-drum rollers)
2.Pneumatic rubber-tired rollers
3.Sheepsfoot rollers
4.Vibratory rollers
54
 Filed Compaction

Compaction Equipment
Smooth-wheel rollers are suitable for
proof rolling
subgrades and for finishing operation
of fills
with sandy and clayey soils. These
rollers provide 100% coverage under
the wheels, with ground contact
pressures as high as 310 to 380
kN/m^2. They are not suitable for
55
producing high unit weights of
compaction when used on thicker
 Compaction Equipment
Smooth-wheel
rollers
o one steel
drum and
rubber tired
drive wheels
o two steel drums
one of which is
the driver
o effective for
gravel, sand, 56

silt soils
 Compaction Equipment

Pneumatic rubber-tired rollers

Pneumatic rubber-tired rollers are
better in many respects than the
smooth-wheel rollers. The former are
heavily loaded with several rows of
tires.
These tires are closely spaced—four
to six in a row.
Pneumatic rollers can be used for
sandy and clayey soil compaction.
57
Compaction is achieved by a
 Compaction Equipment

Pneumatic rubber-
tired rollers

58
 Compaction Equipment

Sheepsfoot rollers
Sheepsfoot rollers are drums with a
large number of projections.
The area of each projection
may range from 25 to 85 cm2. These
rollers are most effective in
compacting clayey soils. The contact
pressure under the projections can
range from 1400 to 7000 kN/m2.
59
 Compaction Equipment

Sheepsfoot rollers
During compaction in the field, the
initial passes compact the lower
portion of a lift.
Compaction at the top and
middle of a lift is done at a
later stage.

60
 Compaction Equipment

Sheepsfoot
rollers

61
 Compaction Equipment

Vibratory rollers
Vibratory rollers are extremely
efficient in compacting granular
soils. Vibrators can be attached to
smooth-wheel, pneumatic rubber-
tired, or sheepsfoot rollers to
provide vibratory effects to the
soil. The vibration is produced by
rotating off-center weights.
62
 Factors Affecting Field
Compaction
For field compaction, soil is spread
in layers and a predetermined
amount of water is
sprayed on each layer (lift) of
soil, after which compaction is
initiated by a desired roller.
In addition to soil type and
moisture content, other factors
must be considered to achieve the 63
desired unit weight of
 Factors Affecting Field
Compaction
These factors include the
thickness of lift,
the intensity of
pressure applied by the
compacting equipment, and the
area over which the pressure is
applied.
These factors are important
because the pressure applied at 64
the surface decreases with depth,
 Factors Affecting Field
Compaction
During compaction, the dry unit
weight of soil also is affected by
the number of roller passes.
The dry unit weight of a soil at
a given moisture content
increases to a certain point with
the number of roller passes.

65
 Specifications for Field
Compaction
In most specifications for
earthwork, the contractor is
instructed to achieve a
compacted field dry unit
weight of 90
to 95% of the
maximum dry unit weight
determined in the laboratory
by either the standard or
modified Proctor test. 66
 Specifications for Field
Compaction
This is a specification for
relative compaction, which
y
R = dfiel × 100
can be expressed as
% ydd max
lab
where R = relative compaction
For the compaction of granular soils,
specifications sometimes are written in
terms of the required relative
density Dr or the required relative
compaction.
67
 Specifications for Field
Compaction
Relative density should not
be confused with relative
compaction.
Ro
R (R) and the relative
Correlation between relative

= 1 − D r 1−
compaction
R
yd(min
wher
density Dr
e: o
)
R =y
o
d
max
68
Determination of Field Unit
Weight of Compaction
When the compaction work is
progressing in the field, knowing
whether the specified unit
weight has been achieved is
useful.
The standard procedures for
determining the field unit weight
of compaction include
1.Sand cone method 69
2.Rubber balloon method
 Sand Cone Method

Sand Cone Method (ASTM Designation

D-1556)
The sand cone device consists of a
glass or plastic jar with a metal cone
attached at its top

70
Determination of Field Unit
Weight of Compaction

Nuclear Rubber
Method Balloon
method 71
 Worked Examples
Example 1
The results of a standard Proctor test
are given in the following table.
Determine the maximum dry unit weight
of compaction and the optimum
Also, determine
moisture content required to the
(γdry)max .
achieve 95%
Volume of Proctor
of 944 944 944 944 944 944 944
944
Mold (cm^3 )
Mass of wet soil in the 1.68 1.71 1.77 1.83 1.86 1.88 1.87 1.85
mold ( kg)
Water content ( % ) 9.9 10.6 12.1 13.8 15.1 17.4 19.4 21.2

72
 Worked Examples
Example 2
Given
1)The in situ void ratio of a borrow pit’s soil
is 0.72.
2)The borrow pit soil is to be excavated and
transported to fill a construction site where
it will be compacted to a void ratio of 0.42.
3)The construction project required
10000 m^3 of compacted soil fill
Required
Volume of soil that must be excavated from
the borrow pit to provide the required
73
volume of fill.