compaction

1. Sanjivani Rural Education Society's
Sanjivani College of Engineering, Kopargaon 423603.
Department of Civil Engineering
Sub –Soil Mechanics
S. Y. B Tech Civil, Semester –I
Topic-
Unit-3 –Compaction
By,
Prof. A. V. Ghogare
(Assistant Professor)
Mail Id- ghogareamolcivil@sanjivani.org.in

2. 2
Compaction Consolidation
soil particles are packed more
closely together by mechanical
means
soil particles are packed more closely
together under the application of static
loading
It is achieved through reduction of air
voids.
It is achieved through gradual drainage
of water from soil pores.
It is a rapid process. It is a gradual process. In some soils it
takes many years.
It is an artificial process. It is a natural process.
Proper compaction of soil is achieved
at optimum moisture content.
Consolidation is strictly applicable for
saturated or nearly saturated clays or
soils with low permeability.
Comparison between Compaction and Consolidation:

3. 3
Laboratory Compaction
The variation in compaction with water content and
compactive effort is first determined in the laboratory.
There are several tests with standard procedures such as:
• Indian Standard Light Compaction Test (similar to
Standard Proctor Test)
• Indian Standard Heavy Compaction Test (similar to
Modified Proctor Test)

4. 4
Dry Density - Water Content Relationship
The laboratory testing is meant to establish the maximum dry density
that can be attained for a given soil with a standard amount of
compactive effort.

5. 5
Dry density can be related to water content and degree
of saturation (S) as
dry density can be related to percentage air voids (na) as
The relation between moisture content and dry unit weight
for a saturated soil is the zero air-voids line. It is not
feasible to expel air completely by compaction, no matter
how much compactive effort is used and in whatever
manner.

6. 6
Factors Affecting Compaction
The factors that influence the achieved degree of
compaction in the laboratory are:
 Water content
 Compactive effort
 Plasticity of the soil
 Effect of method of compaction
 Effect of type of soil
 Addition of admixtures

7. 7
Effect of Increasing Water Content
 As water is added to a soil at low moisture contents, it
becomes easier for the particles to move past one
another during the application of compacting force.
 The particles come closer, the voids are reduced and this
causes the dry density to increase.
 As the water content increases, the soil particles develop
larger water films around them
 The maximum dry density(MDD) occurs at an optimum
water content (OMC), and their values can be obtained
from the plot.

8. 8
Effect of Increasing Compactive Effort
 The effect of increasing compactive effort is shown. Different
curves are obtained for different compactive efforts.
 greater compactive effort reduces the optimum moisture
content and increases the maximum dry density.
 An increase in compactive effort produces a very large
increase in dry density for soil when it is compacted at water
contents drier than the optimum moisture content

9. 9
Compaction of Cohesionless Soils
 For cohesionless soils (or soils without any fines), the
standard compaction tests are difficult to perform.
 For compaction, application of vibrations is the most
effective method.
 Watering is another method.
 The seepage force of water percolating through a
cohesionless soil makes the soil grains occupy a more
stable position
• For these soil types, it is usual to specify a
magnitude of relative density (ID) that must be
achieved.
• If e is the current void ratio or gd is the current dry
density, the relative density is usually defined in
percentage as

10. 10
where emax and emin are the maximum and minimum void
ratios that can be determined from standard tests in the
laboratory, and ᵧdmin and ᵧdmax are the respective minimum
and maximum dry densities On the basis of relative density,
sands and gravels can be grouped into different categories:

11. 11

12. 12
Effect of method of compaction
The dry density achieved by the soil depends on the
following characteristics of compacting method.
 Weight of compacting equipment
 Type of compaction
 Area of contact of
 Time of exposure
 Each of these approaches will yield different
compactive effort. Further, suitability of a particular
method depends on type of soil.

13. 13
Field Compaction Equipment
There is a wide range of compaction equipment. The compaction
achieved will depend on the thickness of lift (or layer), the type of
roller, the no. of passes of the roller, and the intensity of pressure on the
soil. The selection of equipment depends on the soil type as indicated.

14. 14
Modified Compaction Test

15. 15
Field Compaction Control-
It is extremely important to understand the factors affecting
compaction in the field and to estimate the correlation between
laboratory and field compaction. Field compaction control depends on
(i) Placement wate rcontent,
(ii) Type of equipment for compaction
(iii) Lift thickness
(iv) Number of passes based on soil type & degree of compaction
desired Placement water content is the water content at which the
ground is compacted in the field

16. 16
 Used for rapid determination of water content of soil in
field.
 Rapid moisture meter is used as an alternative.
 Proctor‟s needle consists of a point, attached to
graduated needle shank and spring loaded plunger.
 Varying cross sections of needle points are available.
 The penetration force is read on stem at top.
 To use the needle in field Calibration in done on the
specific soil in lab and calibration curve is prepared and
the curve is used in the field to determine placement
water content.