Soil Compaction
Compaction, in general, is the densification of soil by
removal of air, which requires mechanical energy.
The degree of compaction of a soil is measured in terms of its
dry unit weight. When water is added to the soil during
compaction, it acts as a softening agent on the soil particles.
The soil particles slip over each other and move into a
densely packed position. The dry unit weight after
compaction first increases as the moisture content
increases.
Soil Compaction
Laboratory Tests for
Compaction
Standard Proctor
Test
Soil Compaction
Soil Compaction
Standard Proctor
Test
Soil Compaction
Standard Proctor
Test
Soil Compaction
Standard Proctor
Test
Soil Compaction
Soil Compaction
Soil Compaction
Soil Compaction
Soil Compaction
Soil Compaction
Modified Standard Proctor
Test
For conducting the modified Proctor test, the same mold is used with a
volume of 944 cm3 (1/30 ft 3), as in the case of the standard Proctortest.
However, the soil is compacted in five layers by a hammer that has a
mass of 4.54 kg (10 lb).
The drop of the hammer is 457 mm (18 in.). The number of hammer
blows for each layer is kept at 25 as in the case of the standard Proctor
test.
Because it increases the compactive effort, the modified Proctor test
results in an increase in the maximum dry unit weight of the soil. The
increase in the maximum dry unit weight is accompanied by a decrease
in the optimum moisture content.
Soil Compaction
Modified Standard Proctor
Test
Soil Compaction
Field 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
Soil Compaction
Field Compaction
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 (45 to 55 lb/in2). They are not suitable for producing high unit
weights of compaction when used on thicker layers.
Soil Compaction
Field Compaction
Soil Compaction
Field Compaction
Soil Compaction
Field Compaction
Soil Compaction
Factors affecting 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 the surface decreases with depth, which
results in a decrease in the degree of soil
compaction.
Soil Compaction
Factors affecting Compaction
the dry unit weight of soil also is affected by the
number of roller passes
Soil Compaction
Field Specification for
Compaction
Soil Compaction
Sand Cone replacement method for in-situ
soil density
The sand cone device consists of a glass or plastic jar with a
metal cone attached at its top. The jar is filled with uniform
dry Ottawa sand. The combined weight of the jar, the cone,
and the sand filling the jar is determined (W 1 ).
In the field, a small hole is excavated in the area where the
soil has been compacted. If the weight of the moist soil
excavated from the hole (W 2 ) is determined and the
moisture content of the excavated soil is known, the dry
weight of the soil can be obtained as
Soil Compaction
After excavation of the hole, the cone with the sand-filled
jar attached to it is inverted and placed over the hole .
Sand is allowed to flow out of the jar to fill the hole and
the cone. After that, the combined weight of the jar, the
cone, and the remaining sand in the jar is determined (W
4 ), so
Soil Compaction
Soil Compaction
Example
s:
Prob. 1: The maximum dry density and optimum moisture content of a soil
from standard proctor’s test are 18 kN/m 3 and 16% respectively. Compute the
degree of saturation of the sample, assuming the specific gravity of soil grains
as 2.70.
Prob. 2: The wet weight of a sample is missing in a Proctor test. The oven-dry
weight of this sample is189 N. The volume of the mould used is 1000 cm 3 . If
the degree of saturation of this sample is 90%, determine its water content and
bulk density.
Prob. 3: A soil in the borrow pit has a water content of 11.7% and the dry
density of 16.65 kN/m 3 . If 2,070 m 3 of soil is excavated from it and
compacted in an embankment at a porosity of 0.33, calculate the compacted
volume of the bankment that can be constructed out of this volume of soil.
Soil Compaction
Example
s:
Soil Compaction
Example
s:
Prob. 4: The soil from a borrow pit is at a bulk density of 17.10 kN/m 3 and a
water content of 12.6%. It is desired to construct an embankment with a compacted
unit weight of 19.62 kN/m 3 at a water content of 18%. Determine the quantity of
soil to be excavated from the barrow pit and the amount of water to be
added for every 100 m 3 of compacted soil in the embankment.
