The document discusses predicting swelling pressure of expansive soils using compositional and environmental factors. Expansive soils exhibit significant volume changes with moisture content variations, which can damage foundations. Directly determining swelling characteristics is expensive. The paper investigates how soil state (reflected by initial moisture content, dry density, and surcharge pressure) and soil type (reflected by liquid limit and plasticity index) influence predicted swelling pressure. 46 free swell oedometer tests were conducted on 4 soils, varying one factor at a time over practical ranges. Results show swelling pressure is associated with both compositional and environmental factors.

1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
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PREDICTION OF SWELLING PRESSURE OF EXPANSIVE SOILS
USING COMPOSITIONAL AND ENVIRONMENTAL FACTORS
Dr. Ch. Sudha Rani 1
1
Associate Professor, Dept of Civil Engineering, Sri Venkateswara University, Tirupati,
India-517502
ABSTRACT
Expansive soils exhibit significant volume changes with variations in soil moisture
content. Foundations constructed on these soils are subjected to considerable damage due to
swelling. Determination of swelling characteristics (Swelling Pressure, Swell Potential and
Swell Index) is a prerequisite for safe and economic design of structures resting on expansive
soils. Direct determination of swelling characteristics is expensive in terms of time, money
and services experts and skilled technicians. Hence geotechnical engineers have always been
striving to evolve simple methods to predict the soil behaviour considering the soil state or
soil type. This paper investigates the influence of both soil state and soil type on prediction of
swelling pressure. The soil state is reflected by environmental factors namely initial Moisture
Content, in-situ Dry Density and Initial Surcharge Pressure whereas the soil type is reflected
by the compositional parameters namely Liquid Limit and Plasticity Index.
KEYWORDS: Expansive soils, Soil state, Soil type, Swelling Pressure, Swell Potential,
Swell Index
1. INTRODUCTION
The expansive clayey soil deposits are highly moisture sensitive with respect to stress,
deformation and strength. These soils exhibit extreme variation in strength and deformation
such as heaving, settlement and shrinkage as the Moisture Content alters. Many attempts
have been made in the past to identify Expansive Soils and to analyze the factors affecting the
swelling of clayey soils based on simple laboratory and field test results (Altmeyer 1953,
Holtz and Gibbs 1956, Holtz 1959, Ranganathan and Sathyanarayana 1965, , USBR 973,
Chen 1975, Dakshinamurthy and Raman 1977, Dinesh Mohan 1977, Anon 1981, Sridharan
et.al. 1986). Swelling Pressure, Swell Potential, and Swelling Index are identified as three
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important swelling characteristics which are required for assessment of heave and for safe
and economic design of foundations resting on Expansive soils. Numerous methods have
been proposed in the literature for direct laboratory measurement of swelling characteristics
from one dimensional Consolidometer tests (Holtz 1959, Seed et al.1962, Sridharan et.al.
1986, Chen 1988). Several attempts have been made in the past to establish meaningful
correlations between swelling characteristics and index properties. Such correlations are
believed to be helpful in situations where time and money are constraints. Liquid limit,
Plasticity Index, Colloid Content, Suction Pressure, Surcharge Pressure, In-situ Dry Density,
and In-situ Moisture Content are some of the factors that are used in the past to predict
Swelling Pressure and Swelling Potential. Some of these factors are dependent on
composition of the soil (Liquid limit, Plasticity Index, Colloid Content) while others are
environmental Factors (In-situ Dry Density, In-situ Moisture Content, and Surcharge
Pressure). The basic motivating factor behind inclusion of Atterberg limits and Indices
derived from Atterberg limits is the fact that both Atterberg limits and Engineering properties
are dependent on composition of the soil. The engineering properties of soils are now said to
be dependent on the composite effect of compositional and environmental factors (Mitchell,
1993). Liquid Limit and Plasticity Index are known to reflect compositional factors while in-
situ Dry Density and natural Moisture Content are the important environmental factors that
influence the engineering properties significantly (Mallikarjuna Rao et. al.2006).
Swelling Pressure, defined as the pressure which is required to return a swelled
specimen back to its original state prior to swelling, and is one of the important swelling
characteristics. Swelling Pressure is necessary for estimation of heave and for safe and
economic design of Canal linings. Several investigators attempted to develop correlations for
prediction of swelling characteristics in terms of either compositional factors or
environmental factors or Combination of both (Komarnik & David 1969, Vijayvergiya &
Ghazzaly 1973, Nayak & Christensen 1974, Yusuf Erzin 2004). Although these models are
acceptable for soils based on which the models were developed and their use in general for all
soils are not acceptable. General applicability of these methods is more dependent on
whether all the influencing factors are accounted for in the proposed regression model or not.
Hence, there is a need to understand the influence of each of the compositional factors and
environmental factors on swelling characteristics, in order to develop meaningful correlations
having more general applicability. The objective of this investigation is to assess the degree
of association between Swelling Pressure and each of the influencing parameters namely
Liquid limit (wL),Plasticity Index (IP), Initial Dry Density (γd), Initial Surcharge Pressure (Sc)
and Initial Moisture Content (mc).
2.0 EXPERIMENTAL INVESTIGATION
Representative but disturbed expansive soil samples from four different parts of India
are collected from open trial pits at depths ranging from 2.5m to 3.0m. The index properties
of soils used, placement conditions and Compression Index of all soils tested are presented in
Table 1. From Table 1 it can be observed that for the soil samples tested, the Liquid Limit is
ranging from 50% to 120%, and Plasticity Index is ranging from 24% to 88%. The range of
each of the parameters considered is so wide that it covers practically most of the soils that
are likely to be encountered in general practice. The four soils used in this investigation are
designated as SS1, SS2, SS3, and SS4 for convenience.

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Three series of free swell oedometer tests are conducted on all the four soils varying
the three placement conditions (Initial Moisture Content, Initial Dry Density, Initial
Surcharge Pressure), one at a time over a practical range while keeping the other two factors
at one particular level. In all 46 free swell oedometer tests were conducted and Swelling
Pressure (PS) is obtained from the e-log p plots.
Table 1 Properties of Tested Soils
3.0 RESULTS AND DISCUSSIONS
Typical e-log p plots obtained from free swell oedometer tests are shown in Fig.1.
Swell Pressure (PS) is obtained from these plots in accordance with the relevant I.S. codes of
Practice. All the test results are summarized in Table 2.
Fig. 1 Typical e-log p Curves from Free Swell Odometer Tests
Properties SS1 SS2 SS3 SS4
Gravel (%) 0% 0.6 % 0.4 % 1 %
Sand (%) 5% 5.2% 4.4% 4.8%
Silt + Clay (%) 95% 94.2% 95.2% 94.2%
Liquid Limit (WL) 120% 69% 56% 48%
Plastic Limit (WP) 32% 36.9% 30.81% 21.47%
Plasticity Index (IP) 88% 32.1% 25.19% 23.61%
Free Swell Index (FSI) 275% 120% 90% 75%
Shrinkage Limit (WS) 8.5 9% 11% 13.5%
I.S Classification CH CH CH CI
Specific Gravity (Gs) 2.75 2.78 2.81 2.87
Degree of Expansion VH H M M

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Table 2 Details and Results of Tests conducted
S.No
Soil
Design
ation
Atterberg Limits Placement Conditions
Swelling
Pressure
( Ps)
Kpa
Plastic
Limit
(WP)
(%)
Liquid
Limit
(WL)
(%)
Plasticity
Index
(IP) (%)
Initial Dry
Density
γd (kN/m3
)
Initial
Moisture
Content
(mc)
(%)
Initial
Surcharge
(Si)
(kPa)
1 SS1 32.00 120.00 88.00 13.50 0.00 5.00 330.00
2 SS1 32.00 120.00 88.00 14.50 0.00 5.00 470.00
3 SS1 32.00 120.00 88.00 15.50 0.00 5.00 680.00
4 SS1 32.00 120.00 88.00 16.50 0.00 5.00 950.00
5 SS1 32.00 120.00 88.00 16.00 0.00 5.00 810.00
6 SS1 32.00 120.00 88.00 17.00 0.00 5.00 1120.00
7 SS2 36.90 69.00 32.10 14.00 0.00 5.00 170.00
8 SS2 36.90 69.00 32.10 16.00 0.00 5.00 300.00
9 SS2 36.90 69.00 32.10 17.50 0.00 5.00 640.00
10 SS2 36.90 69.00 32.10 18.50 0.00 5.00 700.00
11 SS3 30.81 56.00 25.19 14.00 0.00 5.00 160.00
12 SS3 30.81 56.00 25.19 16.00 0.00 5.00 260.00
13 SS3 30.81 56.00 25.19 17.50 0.00 5.00 410.00
14 SS4 21.47 48.00 26.53 14.00 0.00 5.00 99.00
15 SS4 21.47 48.00 26.53 16.00 0.00 5.00 240.00
16 SS4 21.47 48.00 26.53 17.50 0.00 5.00 380.00
17 SS1 32.00 120.00 88.00 16.00 16.00 5.00 410.00
18 SS1 32.00 120.00 88.00 16.00 20.00 5.00 350.00
19 SS1 32.00 120.00 88.00 16.00 24.00 5.00 300.00
20 SS1 32.00 120.00 88.00 16.00 28.00 5.00 250.00
21 SS2 36.90 69.00 32.10 16.00 7.00 5.00 290.00
22 SS2 36.90 69.00 32.10 16.00 15.00 5.00 210.00
23 SS2 36.90 69.00 32.10 16.00 20.00 5.00 190.00
24 SS2 36.90 69.00 32.10 16.00 25.00 5.00 100.00

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S.N
o
Soil
Designa
tion
Atterberg Limits Placement Conditions
Swelling
Pressure
( Ps)
kPa
Plastic
Limit
(WP)
(%)
Liquid
Limit
(WL)
(%)
Plasticity
Index
(IP) (%)
Initial Dry
Density
γd (kN/m3
)
Initial
Moisture
Content
(mc) (%)
Initial
Surcharge
(Si)
(kPa)
25 SS2 36.90 69.00 32.10 16.00 35.00 5.00 60.00
26 SS3 30.81 56.00 25.19 16.00 15.00 5.00 135.00
27 SS3 30.81 56.00 25.19 16.00 22.00 5.00 120.00
28 SS3 30.81 56.00 25.19 16.00 30.00 5.00 65.00
29 SS4 21.47 48.00 26.53 16.00 6.00 5.00 180.00
30 SS4 21.47 48.00 26.53 16.00 15.00 5.00 120.00
31 SS4 21.47 48.00 26.53 16.00 20.00 5.00 100.00
32 SS4 21.47 48.00 26.53 16.00 25.00 5.00 72.00
33 SS1 32.00 120.00 88.00 16.00 0.00 20.00 710.00
34 SS1 32.00 120.00 88.00 16.00 0.00 40.00 600.00
35 SS1 32.00 120.00 88.00 16.00 0.00 60.00 510.00
36 SS1 32.00 120.00 88.00 16.00 0.00 80.00 430.00
37 SS2 36.90 69.00 32.10 16.00 0.00 15.00 200.00
38 SS2 36.90 69.00 32.10 16.00 0.00 30.00 190.00
39 SS2 36.90 69.00 32.10 16.00 0.00 60.00 160.00
40 SS2 36.90 69.00 32.10 16.00 0.00 100.00 140.00
41 SS2 36.90 69.00 32.10 16.00 0.00 150.00 100.00
42 SS3 30.81 56.00 25.19 16.00 0.00 20.00 210.00
43 SS3 30.81 56.00 25.19 16.00 0.00 55.00 140.00
44 SS3 30.81 56.00 25.19 16.00 0.00 110.00 110.00
45 SS4 21.47 48.00 26.53 16.00 0.00 40.00 185.00
46 SS4 21.47 48.00 26.53 16.00 0.00 80.00 150.00

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4.0 REGRESSION MODEL FOR PREDICTION OF SWELLING PRESSURE
Based on the test results presented in Table 2 it can be concluded that the Swelling
Pressure is dependent on all the placement conditions namely initial Moisture Content, initial
Dry Density and initial Surcharge Pressure and also the Liquid Limit and Plasticity Index of
the soil. Placement conditions reflect environmental factors whereas Liquid Limit and
Plasticity Index reflect compositional factors. Hence Swelling Pressure can be said to be
dependent on both environmental factors and compositional factors and may be expressed as
given below.
PS = f ((wL, IP, γd, mc, Si) … (1)
Swelling Pressure is observed to bear a nonlinear relationship with all the influencing
factors (γd, mc and Si) as the Swelling Pressure is observed to increase more sharply with Dry
Density than with mc and Si. Hence no linear relationship between the independent and
dependent variable is possible. In order to make the relationship linear, logarithm of Swelling
Pressure (Log PS) and logarithm of initial Dry Density (Log γd) are considered in the
development of relationships. Hence, the functional relationship between Swelling Pressure
and initial Moisture Content, initial Dry Density, initial Surcharge, Liquid Limit and
Plasticity Index can be expressed as given below.
Log (PS) = ( ) ( ) ( ) ( ) ( )( )Sa5ma4a3a2a1a ic0 +++++ dPL LogIW γ … (2)
The numerical values of regression coefficients a0, a1, a2, a3, a4 and a5 can be obtained
from multiple regression analysis. Microsoft-Excel software provides a subroutine for
multiple regression analysis and the same is used here to obtain the regression coefficients a0,
a1, a2, a3, a4 and a5 as well as the regression model and correlation coefficient, R2
. The
regression model so obtained is given below
Log (PS) = ((-4.3341) + (0.0071*WL) + (0.0006*IP) +
(5l.2802*Log (γd)) - (1.7900*mc) - (0.0037*Si)) … (3)
Where
γd = Initial Dry Density in kN/m3
mc = Initial Moisture Content in fraction
wL = Liquid Limit (%)
IP = Plasticity Index (%)
Si = Initial Surcharge Pressure kPa
Swelling Pressure can be predicted using above equation knowing the placement
conditions, Liquid Limit and Plasticity Index. The regression analysis yielded a correlation
coefficient of 0.979 indicating good correlation between the variables and the Swelling
Pressure. Any attempt to correlate Swelling Pressure with either compositional factors alone
or environmental factors alone or any other combination other than the one presented in
equation (3) did not yield any fruitful regression models. Hence the same were not presented
here.

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5.0 APPLICABILITY OF THE PROPOSED CORRELATION
The applicability of the proposed correlation for Swelling Pressure is assessed by
comparing the predicted values of Swelling Pressure for the results reported in this
investigation as well as using the test results reported in the literature. The Swelling Pressure
so predicted is plotted against observed Swelling Pressure for the results of this investigation
and for the reported data. These plots are shown in Figs. 7 and 8. The solid lines in these plots
indicate the line of equality. The points are found to fall close to the line of equality in case of
results of this investigation indicating good prediction. This is expected because it is the data
used for development of proposed regression model However, for other’s data, though many
points are falling close to the line of equality, some of the points are dispersed away from line
of equality. In other words, prediction is good for many soils but not for all soils. This may be
attributed to the fact that coarse fraction which can influence swelling characteristics has not
been accounted for in the proposed regression model. In all the four soils namely SS1, SS2,
SS3 and SS4 the coarse fraction is less than 5%, hence the proposed regression models are
valid only if coarse fraction is less than 5%. Therefore, there is a need to modify the
regression model developed in order to account for the coarse fraction.
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200 1400
SwellingPressure(Predicted)kPa
Swelling Pressure (Observed) kPa
Fig. 2 Observed Vs Predicted Swelling Pressure
(Results of Present Investigation)

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0
200
400
600
800
1000
1200
1400
1600
1800
0 200 400 600 800 1000 1200 1400 1600 1800
SwellingPressure(Predicted)kPa
Swelling Pressure (Observed) kPa
Fig. 3 Observed Vs Predicted Swelling Pressure (Literature data)
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