This document presents the results of an experimental investigation on using a cohesive non-swelling (CNS) layer to inhibit the swelling pressure of black cotton soil (BC soil). Various tests were conducted on BC soil and potential CNS materials to evaluate their properties. Large scale tests with different CNS layer thicknesses showed that swelling deformation decreases with increased thickness. While a CNS layer is effective, its mechanism of inhibiting swelling is not fully understood and depends on factors beyond just dead weight. The study aims to better understand the interaction between CNS layer and expansive soil.

1. BLDEA’S VACHANA PITAMAHA DR.P.G. HALAKATTI COLLEGE OF
ENGINEERING AND TECHNOLOGY , VIJAYAPUR.
DEPARTMENT OF CIVIL ENGINEERING
PRESENTATION ON
“EXPERIMENTAL INVESTIGATION ON COHESIVE NON-SWELLING LAYER”
UNDER THE GUIDANCE OF
DR. S G PATIL
PRESENTED BY :
JAYAPRAKASH HADIMANI
SAGAR BILOOR
SOUBHAGYA S VASTRAD
SNEHA S GUNJIGANVI

2. TABLE OF CONTENTS
1. INTRODUCTION
2. EXECUTIVE SUMMARY
3. OBJECTIVES
4. MATERIALS
5. METHODOLOGY
6. CONCLUSION

3. INTRODUCTION
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• Major portions in India are covered with black cotton soil.
• The black cotton soil is hard as long as it is in dry state & possess high bearing capacity, but it loses its
stability completely when it is in wet state.
• Expansive soils swells upon absorption of water & shrinks upon evaporation.
• In summer it is very common to see shrinkage cracks with hexagonal columnar structure.

4. • Because of this alternate swelling , shrinkage & extreme low shear strength ,structures founded on them are
severely damaged.
• The swelling potential depends upon the type of clay mineral, crystal lattice structure, cation exchange
capacity, ability of water absorption , density & water content.
• Among the Illite, kaolinite, & montmorillonite clay minerals , the montmorillonite possesses the greatest
ability to swell by illite.
• The amount of swell generally increases with increase in plasticity index.
• To avoid such swell- shrink problem, various remedial techniques have been proposed, such as soil
replacement, moisture control, application of adequate surcharge pressure, chemical alterations and use of
cohesive non-swelling cushion technology.
• Among the above mentioned techniques the CNS cushion technology implemented in the subgrade,
foundation, and cross- drainage structures has achieved a remarkable effect.

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Causes of swelling
• Rain fall and rise in the ground water table .
• Reducing load condition, such as surcharge loads increases the swell .
• Transmission of moisture with time; moisture transmission through soil is slow and requires weeks and even years to
saturate depending upon the permeability and thickness of stratum .
• Dry density, dense clays will swell more when they are wetted than the same clay at lower density with the same moisture
content.
• Retarding evaporation; by covering the ground with a structure or pavement
• Transpiration; the roots of trees and shrubs can extract considerable quantities of water from surrounding soil
which aggravate the swell as well as shrink problem

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WHAT IS CNS LAYER METHOD ?
In this technique suitable layer of CNS material as impervious soil is selected by conducting various laboratory
tests.
In this soil at 1m depth is replaced with cohesive non-swelling soils (CNS) below the foundation level .
This technique was implemented by Prof. R. K . Katti to reduce the heave and subsequent problems like
cracks along the canal beds ,foundation of buildings .
The CNS layer acts as a protective layer
between BC soil and canal linings.
It prevents the swelling and shrinkage cracks
produced due to the variations in the moisture
content and temperature.

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EXECUTIVE SUMMARY
 In 1978 , Prof.R.K.Katti had developed a technique where in removal of required depth of expansive soil
and replacing it by cohesive non – swelling soil (CNS) layer is done below the foundations .And they have
yielded the satisfactory results by doing so.
 Katti has successfully adopted it for prevention of heave and resultant cracking of canal beds and
linings and recommends it for use in foundation of other infrastructure also .
 the studies indicated that a cohesive non swelling layer may prove to be effective in resisting
swelling pressure of underlying expansive soil.
An attempt is made to evaluate the effect of various thicknesses of CNS layer on swelling and related
characteristics of underlying expansive soil media.
Experiments have been conducted in large scale test in which different thicknesses of CNS layer were
placed on an expansive soil compacted at known initial density and moisture content under controlled
conditions.
The soils were subjected to saturation during which alterations in swelling pressure were recorded.

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 The variation of density, moisture content and shear strength of the soils with depth were observed.
 It is indicated that the swelling deformation decreases with increase in thickness of CNS layer.

9.  Murthy and Praveen (2008) have speculated that CNS layer develops an electrical environment below
the CNS layer and expansive soil interface .
 it also acts as an overburden to the development of an adsorbed water bonds between clay mineral
particles and inhibits the swelling of expansive soils .
 however due to the lack of test data , there is no scientific evidence to account for the mechanism of
adsorbed water bonds effecting swell characteristics of expansive soils .
Thus, it is necessary to understand the interaction between the CNS layer and expansive soil.
 Sahoo and Pradhan (2010) ,had reported that some of the soil materials which do not meet the
specifications of CNS material , have also shown a potential to effectively inhibit the expansive soil.
 They also reported that when the thickness of CNS layer reaches nearly 1.2m , there will not be any heave
produced in the expansive soil ,even under the saturation condition. Though, the swelling pressure of expansive
clay exceeds the dead weight of CNS layer.
This indicates that the swelling inhibition mechanism not only depends on the dead weight of CNS layer
but , also depends on some other factors controlling the swelling of the soil.

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OBJECTIVES
 To inhibit the swelling pressure of BC soil by using CNS layer.
 To determine the suitability of the chosen material to be used as CNS material.
 To determine the thickness of CNS layer based on swelling pressure exerted by underlying BC soil.
 To utilise the waste materials produced in industries in preparing CNS material.
 To prevent the cracks in hydraulic structures and road works.
 To improve the life span of the structures built over BC soils.
 To eliminate unequal settelments of light weight strucures
 To confine the expansive soil to resist the swelling pressure of soil.

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MATERIALS
 Problematic soil that is recognized to have high swelling characteristics
 To prepare a CNS Layer, we require locally available soil, industrial wastes such as fly ash, bottom ash,
cement industries effluents etc.
 CNS material should be non-swelling with a maximum swelling pressure of 10kn/m^2.

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METHODOLOGY
• Various tests are conducted in order to determine the physical & chemical properties of the
expansive soils.
• Because many of the structures fail due to the improper assessment of properties of the
underlying soils.
• In this method the tests are conducted on the BC soils as well as on the chosen waste
material and they are,
1. Particle size distribution.
2. Atterberg limits.
 Liquid limit
 Plastic limit
 Shrinkage limit
3. Standard Proctor test to determine OMC and MDD

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5. Free swell index.
6. Swelling pressure test.
The is code 9451 (1994), has recommended certain specifications for cns soils. If these criterias are satisfied
then only it can be used for further works.
PROPERTIES CRITERIA AND SPECIFICATION RANGE
PARTICLE SIZE ANALYSIS (%) GRAVEL (0-10)
SAND (30-40)
SILT (30-40)
CLAY (15-20)
ATTERBERGS LIMIT (%) PLASTICITY INDEX (15-30)
PLASTIC LIMIT (20-25)
LIQUID LIMIT (30-50)
SWELL PRESSURE (KN/M^2) LESS THAN10
DIFFERENTIAL FREE SWELL TEST (%) <20 (Low)
20-35 (Moderate)
35-50 (High)
>50 (Very high)
Ref: IS 2720-part 40

14.  TESTS PERFORMED:
1. PARTICLE SIZE DISTRIBUTION:
• This is performed to determine the percentage of each size of grain that is contained within a soil sample ,
and the results of the test are used for plotting the grain size distribution curve.
• This information is used to classify the soil and to predict its behaviour.
• The two methods which are generally used for finding the grain size distribution are ,
i. Sieve analysis: It is used for particle sizes larger than 0.075mm in diameter.
ii. Hydrometer analysis: It is used for particle sizes smaller than 0.075mm in diameter.

15.  SIEVE ANALYSIS (DRY ANALYSIS) :
Weight of soil sample taken = 1000 gms.
IS sieve
size(mm)
Empty wt of
sieve
Empty wt of
sieve + soil
Wt of soil
retained on
each soil
% wt of soil
retained
Cumulative
% wt
retained
% wt
passing
4.75 478 508 30 3 3 97
2.36 416 490 74 7.4 10.4 89.6
1.18 444 762 318 31.8 42.2 57.8
0.6 404 595 191 19.1 61.3 38.7
0.425 320 480 160 16 77.3 22.7
0.3 398 464 66 6.6 83.9 16.1
0.15 364 468 104 10.4 94.3 5.7
0.075 398 418 20 2 96.3 3.7
pan 380 418 38 3.8 100.1 -

16. GRAIN SIZE DISTRIBUTION CURVE:
𝐷10 = 0.21
𝐷30= 0.5
𝐷60 = 1.3
Cu =
𝐷60
𝐷10
=
1.3
0.21
= 6.19
Cc =
𝐷30^2
𝐷10×𝐷60
=
0.5×0.5
0.21×1.3
= 0.915
Since Cu >6 and Cc <1,
It can be classified as poorly graded
sand.
0
10
20
30
40
50
60
70
80
90
100
0.01 0.1 1 10
%
FINER
SIEVE SIZES
SIEVE ANALYSIS

17.  WET ANALYSIS:
• In wet analysis 1000gms of soil is soaked in water for a period of 24 hours.
• Later it is sieved through 75 micron IS Sieve. The weight of soil retained on 75 micron is then taken out and
dried in oven.
• The oven dried soil is removed from the oven and it is then analysed for particle size distribution.
IS sieve
size(mm)
Empty wt of
sieve
Empty wt of
sieve + soil
Wt of soil
retained on
each soil
% wt of soil
retained
Cumulative %
wt retained
% wt
passing
4.75 474 476 2 0.2 0.2 99.8
2.36 411 417 6 0.6 0.8 99.2
1.18 440 478 38 3.8 4.6 95.4
0.6 400 425 25 2.5 7.1 92.9
0.425 317 331 14 1.4 8.5 91.5
0.3 396 402 6 0.6 9.1 90.9
0.15 361 370 9 0.9 10 90
0.075 376 381 5 0.5 10.5 89.5
pan 376 1271 895 89.5 100 0

18. GRAIN SIZE DISTRIBUTION CURVE ( WET ANALYSIS):
0
10
20
30
40
50
60
70
80
90
100
110
120
0.01 0.1 1 10
%
FINER
SIEVE SIZES
SIEVE ANALYSIS

19. 2. DETERMINATION OF LIQUID LIMIT ( CONE PENETRATION TEST):
• the liquid limit of soil is the minimum water content at which the soil is still in the liquid state but has a small
shearing strength against the flow.
• The liquid limit corresponds to the water content of a paste which would give 20mm penetration of the soil.
 Observations:
Weight of soil sample , w = 150 gm.
MOISTURE CONTENT (%) PENETRATION (MM)
40 5
46 8
52 12
58 16
72 25

20. LIQUID LIMIT TEST GRAPH :
0
10
20
30
40
50
60
70
80
0 5 10 15 20 25 30
MOISTURE
CONTENT
(%)
PENETRATION(MM)
LIQUID LIMIT TEST
THE MOISTURE CONTENT
CORRESPONDING TO 20MM
PENETRATION IS ,
WL = 65%

21. 3. DETERMINATION OF PLASTIC LIMIT OF SOIL:
• Plastic limit the moisture content at which a fine-grained soil can no longer be remolded without cracking.
• It is the moisture content at which the rolled soil will begin to crumble when rolled into a thread of 3mm.
• It is the boundary between the plastic and semi-solid states of consistency.
 Observation and recordings:
1. Container no. 5.
2. Empty weight = 29.24gm.
3. Empty weight +wet soil = 32.83gm.
4. Empty weight + dry soil = 31.82gm.
 Determination of water content
water content= W = (W2 – W3)/(W3 – W1)
= (32.83 – 31.82)/(31.82 -29.24)x 100 = 39.1 %
Therefore , Wp =39.1 %

22. Plasticity index = IP = WL – WP
= 65 – 39.1
Ip = 25.9 %
Since the plasticity index is 25.9% and liquid limit is 65%, from the plasticity chart the soil can be
classified as High Swelling Silt (MH) .
4. DETERMINATION OF FREE SWELL INDEX:
• Take two 10gm soil specimen of oven dry soil passing through 425 micron IS Sieve.
• Pour each of the specimen in each of the two glass graduated cylinders of 100ml capacity.
• Fill one cylinder with kerosene oil and the other with distilled water up to the 100ml mark. After removal of
entrapped. Air (by gentle shaking or stirring with a glass rod), allow soils in both the cylinders to settle.
• Allow sufficient time (not less than 24hrs) for the soil sample to attain equilibrium state of volume without
any further change in the volume of the soils.
• On completion of swelling, read out the final volume of soils in each of the cylinders.

23. • CALCULATIONS:
Free Swell Index (%) =
swollen volume in water−swollen volume in kerosene
swollen volume in kerosene
=
𝑉𝑑 −𝑉𝑘
𝑉𝑘
× 100
=
17 −9
9
× 100 = 88.9%
Vd = volume of soil specimen read from graduated cylinder containing distilled water.
Vk = volume of soil specimen read from graduated cylinder containing kerosene.
5. SWELLING PRESSURE TEST:
• This is the maximum force per unit area that needs to be applied over a swelling soil to prevent volume
increase.
• A swelling pressure of less than 20 KPA may not be regarded as of much consequence.
 Method used is determining the swelling pressure under a minimum surcharge load.

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CONCLUSION
 While during construction, we should avoid swelling / expansive soils.
 Proper investigation of BC soil and CNS soil is to be done, thickness of CNS material
should be evaluated.
 CNS soil method is good and economical amongst other methods.
 CNS material should be of gravely material.
 The CNS layer will effectively inhibit the characteristics of expansive soils.
 The inhibition effect becomes more remarkable as the thickness of CNS layer increases.

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REFERENCES
1. IS .9451.1994 GUIDELINES FOR LINING OF CANALS IN EXPANSIVE SOILS.
2. JOURNAL OF ROCK MECHANICS AND GEOTECHNICAL ENGINEERING.
3. A STUDY ON SUITABILITY AND THICKNESS OF CNS LAYER FOR CANAL LINING.
4. CONSTRUCTION OF ROADS IN BLACK COTTON SOIL AREAS , U.K.GURU VITTAL, CHIEF SCIENTIST, CSIR-
CENTRAL ROAD RESEARCH INSTITUTE, NEW DELHI.

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