COMPACTION:

Compaction means pressing the soil particles close to each other by mechanical means.
During compaction air is expelled from the void space in the soil mass and thus increasing
mass density.
Purpose of Compaction:
a) Air is expelled.
b) Mass density of soil is increased
c) Shear strength of soil is increased and hence the stability and bearing capacity.
d) Reduce the compressibility and permeability of soil.
Field situation where compaction is required:
a) For the construction of embankments.
b) For the construction of earthen dams.
c) For the construction of highways, runways
d) For the foundation soil in buildings.
STANDARD PROCTOR TEST:

This test provides a relation between the water content and the dry density.
Procedure:
a) Take 3kg of air-dried sample passing through 4.75mm sieve.
b) Apply water to bring water content to about 10% less than the estimated optimum
water content (OWC).
c) Clean the mould and take the mass or weight as M1.
d) Apply grease to the inside of the mould, top of the base plate and inside of the collar.
e) Fit the base plate and collar to the mould.
f) Fill the mould in three equal layers and give 25 blows to each layer using the
rammer having a mass of 2.6kg, dropping from a height of 310mm.
g) Scratch with a spatula every compacted layer before putting the soil for the
succeeding layer.
h) Remove the collar and level the soil till the top of mould.
i) Weight or take the mass of the mould with soil again as M2.
 j) Determine the moisture content of the soil w.
k) Add more water to the soil sample and repeat the whole procedure.
COMPACTION CURVE:
A compaction curve is
plotted between the water
content as abscissa and the
corresponding dry density
as ordinate. It is observed
that dry density initially
increases with an increase
in water content till
maximum dry density is
attained
With further increase in
water content, the dry
density decreases.
The water content
corresponding to
maximum dry density
(M.D.D) i.e.
is known as Optimum Moisture Content (OMC) or Optimum Water Content
(OWC).
At water content lower than the optimum, the soil is stiff and has lot of void spaces. So
the dry density is low. As the water content is increased, the soil particles get lubricated
and slip over each other and move into density packed position and dry density is
increased.
However, at water content more than the OMC, the additional water reduce the dry
density, as it occupies the space that might have been occupied by soil particles.
ZERO-AIR VOID LINE: (100% Saturation Line):
For given water content, theoretical is obtained corresponding to the condition when
there are no air voids (i.e. degree of saturation is 100%).
In this condition, the soil will have no air voids because the air voids will be fully filled with
water.
Compaction methods cannot remove all air voids. Therefore, the soil never becomes fully
saturated. Thus the theoretical is only hypothetical. It can be calculated from equation 1
for any water content if G is known. The line indicating the theoretical maximum dry density
can be plotted along with the compaction curve. It is also known as Zero-Air Void Line or
100% Saturated Line.
MODIFIED PROCTOR TEST:
The procedure for Modified Proctor Test is same as that of Standard Proctor Test except for
the following changes in the equipments.
1) It is used for heavier compaction.
2) Weight of the rammer is 4.89kg and it falls from a height of 450mm.
3) Soil is compacted in 5 layers.
COMPACTION CURVE FOR MODIFIED PROCTOR TEST:

DIFFERENCE BETWEEN STANDARD PROCTOR AND MODIFIED PROCTOR

TEST:

Standard Proctor Test Modified Proctor Test

1) For medium compaction 1) For heavier compaction
2) 2.6kg rammer is used 2) 4.89kg rammer is used.
3) Rammer is falling from a height of 310mm 3) Rammer is falling from a height of 450mm
4) Soil is compacted in 3 layers. 4) Soil is compacted in 5 layers
5) Compactive effort = 592 KJ/m³ 5) The Compactive effort is 4.56 times than
that in standard proctor test. When measured
in KJ/m³ = 2700 KJ/m³
6) Curve mentioned above 6) Curve mentioned above
FACTORS AFFECTING COMPACTION:
The dry density of soil is increased by compaction. The increase in the dry density depends
upon,
a) Water Content: As water content is increased, the dry density also increases till a
maximum value and then starts decreasing. At low water content, the soil is stiff and offers
more resistance to compaction. As the water content is increased, the soil particles get
lubricated. The soil mass becomes more workable and the particles have closer packing. The
dry density of the soil increases with an increase in the water content till the optimum water
content in reached.
b) Method of Soil Compaction:
The dry density achieved depends not only upon the amount of compactive effort but also on
the method of compaction. For the same amount of compactive effort, the dry density will
depend upon whether the method of compaction utilizes kneading action, dynamic action or
static action.
c) Type of Soil: The compaction of soil depends upon the type of soil. In general, coarse
grained soils can be compacted to higher dry density than fine-grained soils.
Cohesive soils have high air voids. These soils attain a relatively lower maximum dry density
as compared with the cohesionless soils. Such soils require more water than cohesionless
soils and therefore the optimum water content is high. Heavy clays of very high plasticity
have very low dry density and very high optimum water content.
d) Amount of Compaction:
The compaction of soil increases with the increase in amount of compactive effort. With
increase in Compactive effort, the optimum water content required for compaction also
decreases.
e) Admixture: The compaction characteristics of soils are improved by adding admixtures
like cement, lime, bitumen etc.
FIELD METHODS OF COMPACTION AND THEIR SUITABILITY:
a) Tamper/Rammer:
A hand operated tamper or rammer consists of a block of iron or stone about 3 to 5 kg in
mass attached to a wooden rod.
It is lifted for a height of 0.30m and dropped on the soil to be compacted.
Mechanical rammer operated by compressed air of 30 to 150kg is also used.
Suitability: Suitable for all inorganic soils and where access is difficult for common rollers
i.e. backfilling of a trench.
b) Rollers:
Different types of rollers are used for the compaction of the soils. The types of rollers are:
i) Smooth Wheeled Roller: Consists of three wheels; two large wheels in the rear and one
small wheel in the front. Mass of smooth wheeled roller is 2 to 15Mg (1000kg = 1Mg).
Suitability: These are used for finishing operations after compaction of fills and for
compacting granular base courses of highways.
ii) Pneumatic – Tyred Rollers: Consists of 9 to 11 wheels fixed on two axles, with the
pneumatic tyres so spaced that a complete coverage is obtained with each pass of the roller.
The gross mass of these rollers is 5 to 200Mg.
Suitability: These rollers are effective for compacting cohesive as well as cohesionless soil.
These rollers are the best type of equipment for general use.
Light rollers are affective for compacting soil layers of thickness upto 15cm, whereas heavy
rollers are useful for thickness upto 30cm.
iii) Sheep-foot Roller: These consist of a hollow drum with a large number of small
projections known as feet. These projections penetrate the soil layers during the rolling
operations and cause compaction. The drum can be filled with water or ballast to increase the
mass. These rollers are available both as a self-propelled unit and a towed unit.
Suitability: These are ideally suited for compaction of cohesive soils.
c) Vibratory Compactors: In vibratory compactors, vibrators are induced in the soil during
compaction. The compactors are available in a variety of forms. When the vibratory is
mounted on a drum, it is called as vibratory roller.
These rollers are available both as pneumatic type and the smooth wheel type.
Suitability: Mainly used to compact granular base courses for highways and runways where
the thickness of layers is small.
DIFFERENCE BETWEEN COMPACTION AND CONSOLIDATION:
SOIL STABILIZATION: The process of improving bearing power of the ordinary soil by
physical or chemical method is called Soil Stabilization.
In Soil Stabilization, various methods are used to modify the properties of a soil so that its
engineering performance is improved.
There are two main ways by which the soil properties can be improved:
a) Improving the soil properties of the existing soil without adding any admixtures:
Compaction and Drainage are the examples, which improve the shear strength of soil.
 b) Improvement of the soil properties with the help of admixtures: Stabilization with
cement, lime, bitumen and chemical are the examples.
Necessity of Soil-Stabilized Road: Naturally occurring soils or existing soils are sometimes
found to be weak against shear stress. Such soils have low bearing capacity. These are
improved by stabilization. Stabilization is used for:
i) It is used to increase the shear strength of the soil
ii) It is used to enhance the stability of slopes in soil
iii) It also reduces the construction cost by making best use of locally available
materials
iv) It increases the density of soil
v) It also increases strength of soil against deformation and displacement of loads.
Methods of Soil Stabilization:
a) Mechanical Soil Stabilization
b) Soil-cement Stabilization
c) Soil-lime Stabilization
d) Stabilization by chemical
e) Stabilization by grouting
f) Stabilization by heating
g) Stabilization by Bitumen.
h) Fly-ash Stabilisation
i) Stabilization by freezing
Mechanical Stabilization of Soil: Mechanical Stabilization means stabilization of soil by
mechanical means without adding any chemical or admixtures.
a) Excavation of subgrade soil should be done by JCB.
b) Pulverization should be done to form fine particles.
c) A specified size of aggregates as per IRC is added in soil to improve soil particles.
The fine particles impart cohesion or binding properties, water retention capacity and
acts as a filler for the voids present in the coarse fraction.
d) Then suitable compaction is done using heavy compaction roller followed by curing.
e) After alternate curing and compaction for minimum 7 days. The road is said to be
stabilized.
f) This type of stabilization is used for cheap roads. It is commonly used for the
construction of sub-bases, bases and also for improving the sub-grade soils having
low bearing capacity.
Uses of Mechanical Stabilisation:
a) Load carrying capacity is increased.
b) Resistance against temperature and moisture changes is improved.
c) This method is used to improve the subgrades of low bearing capacity.
d) It is extensively used in the construction of bases, sub-bases and surfacing of roads.
Soil-Cement stabilization of Roads: In this method, the binding property of Portland
cement is made use of to stabilize an earth roads and such a road is known as Soil-Cement
roads.
Procedure:
a) The road surface is cleared and the top layer of soil is loosened to a depth required to
get the desired thickness of road
b) The lumps are then broken and a pulverised material is obtained. If the lumps are hard
and the material is fairly dry, the use of smooth roller can also be made
c) If any additional soil is required to improve the grading, it should be evenly spread
over the loosened roadway material before the starting of mixing operations
d) The surface is then covered by a layer of cement and the spreading of cement may be
done either by hand or by mechanical spreaders
e) The water in required quantity is then sprinkled and the whole mass is intimately
mixed by suitable equipment in such a way that uniform colour and texture are
obtained
f) The layer is compacted by tamping rollers and the final rolling is done with a self-
propelled smooth tandem roller so as to get a smooth surface.
Uses of Cement Stabilisation:
a) It is weather resistant and strong
b) Used for stabilising sandy and other low plasticity soils.
c) The plastic soil-cement can be used for protection of steep slopes against erosive
action of water.
Soil-Lime stabilization of roads: The process of lime stabilization of soil is more or less
same as cement-soil stabilization except that hydrated lime is used in place of cement. The
quantity of lime is about 5 to 10% by weight and the presence of lime helps in reducing
shrinkage and swelling of soil.
CBR TEST: This is a penetration test developed by California Division of Highways for
design of flexible pavements.
This method considers characteristics of subgrade soil and properties of materials.
The CBR is defined as the ratio of the test load to the standard load expresses as percentage,
for a given penetration of the plunger,

The CBR apparatus consist of a mould 150mm diameter and 175mm high, having a separate
base plate and a collar.
Load is applied by a loading frame through a plunger of 50mm diameter on the specimen in
the mould.
Dial gauges are used to measure the penetration of the plunger. The plunger is made to
penetrate the sample at the rate of 1.25mm/minute.
The test is made on a sample of the subgrade soil in a standard loading device which
measures the load required to cause 2.5mm penetration of a plunger having c/s area of
1960mm². The pressure at 2.5mm penetration is worked out and it is expressed as a
percentage of unit standard pressure. This percentage is known as CBR.
This test is repeated for 5mm penetration and CBR is worked out.
The higher value is adopted. Generally, the value of 2.5mm is higher.
The load penetration curve is drawn as follows:

Generally, the value of penetration obtained is higher for 2.5mm. But if CBR value obtained
of 5mm penetration is higher than 2.5mm, then the test has to be repeated and checked.
The laboratory CBR apparatus consists of a mould 150mm diameter with a base plate and a
collar, a loading frame with cylindrical plunger of 50mm diameter and dial gauges for
measuring the expansion on soaking and the penetration values.

Significance of CBR value: It is considered to be one of the most commonly used and
widely accepted tests. This test is used for analysis of existing pavements layer by layer in
respect of their strength and load carrying capacity.
Drawbacks of the test: This test is essentially an arbitrary strength test and hence cannot be
used to evaluate the soil properties like cohesion or angle of internal friction.
SITE INVESTIGATION AND SUB SOIL EXPLORATION:
Site investigation or soil exploration consists of determining the profile of the natural soil
deposits at the site by taking the soil samples and determining the engineering properties of
soil.
Necessity of Site Investigation or Soil Exploration:
i) To select the type and depth of foundation for a given structure
ii) To determine the bearing capacity of the soil
iii) To establish the probable settlements
iv) To establish ground water table
v) To predict lateral earth pressure against retaining wall.
Types of Exploration:
a) General or Preliminary Exploration:
It is done generally in the form of a few borings or test pits.
Tests are conducted with cone penetrometers etc.
It is used to determine the depth, thickness, and composition etc. of each soil stratum at site.
It is used for small projects.
b) Detailed Exploration:
It involves extensive boring and testing the samples
Field test such as vane shear test, plate load test and permeability tests are conducted.
Gives information such as shear strength, compressibility, density index, permeability etc.
Used for heavy structures like bridge, dam etc.
Methods of Exploration:
The methods of exploration are i) Open Excavation ii) Boring
i) Open Excavation: In this method an open excavation is made to inspect the sub-strata.
The method can be divided into two:
a) Pits and Trenches: The size of the pit should be sufficient to provide working space
(1.2m × 1.2m). The depth of the pit depends upon the requirement of the investigation.
Shallow pits up to a depth of 3m can be made without providing lateral support. For deeper
pits, supports are needed.
Trenches are long shallow pits, used in the exploration of slopes.
b) Drifts and Shafts: Drifts are horizontal tunnels made in the hillside to determine the
nature and structure of the geological formation. It should have a minimum clear dimension
of 1.5m width and 2.0m height in hard rock.
Shafts are large size vertical holes made in the geological formation.
ii) Boring: When the depth of exploration is large, borings are used for exploration. A
vertical bore hole is drilled in the ground to get the information about sub-soil strata. Samples
are taken from the bore hole and tested.
Different methods of boring are:
a) Auger Boring: It consists of a shank with a cross wide handle for turning and having
central tapered feed screw. The auger can be operated manually or mechanically. These are
suitable for advancing holes upto a depth of 3 to 6m in soft soil. The hole is advanced by
turning the cross wire handle and at the same time applying thrust in the downward direction.
When the auger is filled with soil, it is taken out.
If the hole is already driven, another type of auger known as post-hole auger is used for
taking soil sample.
b) Wash Boring: In wash boring, the hole is drilled by first driving a hollow casing about 2
to 3m long and then inserting into it a hollow drilled rod (wash pipe) with a chisel-shaped
chopping bit at its lower end. Water is pumped down the wash pipe at high pressure. The
water and the chopped soil particles rise upwards through the annular space between the drill
rod and the casing and are collected in a tub. The hole is further advanced by alternatively
raising and dropping the chopping bit. Some indication about the changes in strata is
provided by the reaction of the chopping bit as the hole is advanced.
It is also indicated by a change in the colour of the wash water collected in the tub.

c) Rotary Drilling: In this method, the bore hole is advanced by rotating a hollow drill which
has a cutting bit at its lower end. It is operated by a rotary mechanism and an arrangement for
applying downward pressure is also there. A drilling fluid under pressure is introduced
through the drilling rod to the bottom of the hole. The fluid carries the cuttings of the material
penetrated from the bottom of the hole to the ground surface through the annular space
between the drilling rod and the water of the hole. When the soil sample is required to be
taken, the drilling rod is raised.
d) Percussion Drilling: This method is used for making holes in the rocks, boulders etc. In
this method a heavy chisel is alternatively lifted and deposited in a vertical hole. The material
gets pulverised. If the point where the chisel sticks is above the water table, water is added to
the hole. The water forms slurry with the pulverised material.
e) Core Drilling: This method is used drilling holes and for obtaining rock cores. In this
method, a core barrel fitted with a drilling bit is fixed to a hollow drilling rod. As the drilling
rod is rotated, the bit advances and cuts an annular hole around an intact core. The core is
taken out using a core lifter.
CRITERIA FOR DECIDING THE LOCATION AND NUMBER OF TEST PITS AND
BORES
The lateral extent of exploration and the spacing of bore holes depend mainly on the variation
of the strata in the horizontal direction
For small and less important buildings, even one bore hole or a trail pit in the centre may
be sufficient.
For compact buildings, covering an area of 0.4 hectares, there should be atleast 5 bore holes,
one at the centre and four near the corners.
For large multi-storeyed buildings, the bore holes should be drilled at all the corners and
also at the important locations. The spacing between the bore holes is generally kept between
10 to 30m.
For highways, the spacing of bore is between 150m and 300m along the centre line.
Types of Soil Samples:
a) Disturbed Samples: These are the samples in which natural structure of the soil gets
disturbed during sampling. However, these samples represent the composition and the
mineral content of the soil. Disturbed samples can be used to determine the properties
of soil such as grain size, plasticity, specific gravity etc.
b) Undisturbed Samples: These are the samples in which the natural structure of the
soil and the water content are retained. However it may be impossible to get truly
undisturbed sample. From undisturbed samples properties such as shrinkage limit can
be determined.
Filed Identification of Soil:
Following simple tests are used in the field for the rough classification of soil:
a) Dry Strength Test: The prepared soil sample is completely dried in the sun. Its
strength is tested by breaking between fingers. Dry strength or resistance to breaking
is the measure of plasticity. If the dry sample can be easily powdered, it is said to
have low dry strength, whereas if considerable finger pressure is required to break the
lump, it is said to have medium dry strength and if it cannot be powdered at all, it is
said to have a high dry strength. Dry strength is characteristics of clays of high
plasticity.
b) Dilatency (Reaction or Shaking Test): About 5cm³ of soil sample is taken and
enough water is added to nearly saturate it. This soil is placed in open palm of the
 hand and shaken horizontally, striking against the other hand several times. The pat is
then squeezed between the fingers. The appearance and disappearance of water with
shaking and squeezing is referred to as a positive reaction. This reaction is called
quick, if water appears and disappears rapidly and it is called slow reaction if water
appears and disappears slowly and no reaction if water does not appear. Inorganic soil
exhibit quick reaction.
c) Toughness Test (Consistency near plastic limit): The moisture content of the soil is
reduced by rolling and re-rolling in to 3mm diameter thread till it reaches plastic limit.
The resistance to moulding at the plastic limit is called Toughness. After the thread
crumbles, lump also crumbles. If the lump can still be moulded slightly drier than the
plastic limit and if high pressure is required to roll the thread between the palms of the
hand, the soil is said to have high toughness.
Medium toughness is indicated by a medium thread. Low toughness is indicated by a
medium thread that breaks easily and cannot be lumped when dried than plastic limit.
BOARD QUESTIONS:
a) Explain the Standard proctor test in detail. Also show the nature of the graph.
b) Difference between Standard Proctor Test and Modified Proctor Test.
c) Define Zero Air Voids Line
d) State and explain the field compaction methods.
e) State and explain the factors affecting compaction
f) State the difference between compaction and consolidation
g) State the types of soil stabilisation and explain any 1 in detail
h) Explain various types of soil stabilisation methods.
i) Explain CBR test with neat Sketches.
j) State any 4 necessities of site investigation
k) Define disturbed and undisturbed soil sample
l) State methods of exploration and explain any one of them
m) State the tests for field identification of soil and explain any one.
n) State criteria for deciding the location and number of test pits and bore holes.
o) What is dilatancy?
p) Define soil exploration

Numerical:
a) Calculate active earth pressure and passive earth pressure at depth of 9m in dry

cohesionless soil with an angle of internal friction of 30⁰ and unit weight of 17kn/m³
b) Compute the intensities of active earth pressure and passive earth pressure at depth of

8m in dry cohesionless soil with an angle of internal friction of 30⁰ and unit weight of
20kn/m³
c) A retaining wall 6m high has a smooth vertical back. The backfill is horizontal. There

is a uniformly distributes load of 3.6t/m² over the back fill. Take r = 1.8t/m³, ø = 30⁰
and C = 0. Determine the magnitude of active earth pressure.
d) The following are the results of standard proctor test performed on a sample of soil.
Find OMC and MDD by plotting graph.
Water content % 5 10 15 20 25
Bulk Density (g/cc) 1.6 1.82 1.90 1.84 1.75

e) The following observations were made using standard proctor test on a soil sample.
Bulk density (g/cc) 1.75 1.95 2.1 2.2 2.15 2.05
Water content % 5 10 15 20 25 30
f)

g)