ejge paper 2004 -0476

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Yusuf ErzinCumhuriyet University, Faculty of Engineering,

Department of Civil Engineering, Sivas, Turkey

e-mail: [email protected]

and

Orhan ErolProfessor of Civil Engineering, Middle East Technical University, 06531 Ankara, Turkey

e-mail: [email protected]

Investigations are reported which aimed at developing an equation for quick

prediction of swell pressures from easily determined soil properties. Bentonite-

Kaolinite clay mixtures were prepared to obtain soils in a wide range of plasticity

indices. A total of 80 constant volume swell tests in oedometers were performed on

statically compacted specimens with varying properties. Swell pressure--plasticity

index--water content--dry density interrelationships were evaluated. Swell pressure

is correlated to the soil properties, namely, plasticity index, water content, liquidity

index and dry density, using multiple regression analyses. The analyses have

confirmed the existence of strong correlations between the swell pressure and the

soil properties. The correlations revealed a simple regression equation for a quick

prediction of swell pressures from easily determined soil properties.

KEYWORDS: Swell pressure, soil properties, plasticity index, expansive soil.

Expansive soils are that clay soils which exhibit significant volume changes because of soil

moisture variation. Expansive soils are a worldwide problem that poses several challenges for civil

engineers. Foundations constructed on these clays are subjected to large uplift forces caused by

swelling, and inducing heaving, cracking, and break up of both building foundations and slabs on

grade members. Heave problems account for more economic loss than all other soil problems. The

paper 2004 -0476 http://www.ejge.com/2004/Ppr0476/Ppr0476.ht

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cost of damages arising from expansive soil problems in the United States alone amounts to $2.3

billion annualy (Dhowian et al., 1988).

The swelling of soils, in general, is due to the presence of expanding clay minerals, hydration of

cations on clay surfaces, and release of intrinsic stresses caused by overconsolidation or

dessication of soils (Dhowian et al., 1988).

Many investigations were carried out to analyse the factors affecting the swelling of clayey soils

(Komornik and David, 1969; El-Sohby and El-Sayed, 1981, 1983; Al-Mhaidib, 1999; Azam and

Abduljauwad, 2000). The major factors affecting the swelling of such soils are mainly concerned

with the physical properties of the particles and the mass of soil, such as initial water content, type

of clay mineral, initial dry density, clay content, type of coarse grained fraction (El-Sohby and El-

Sayed, 1981).

It is of the purpose of this paper to investigate an equation for a quick prediction of swell pressures

of clayey soils from easily determined some soil properties. For this reason, Bentonite-Kaolinite

clay mixtures were prepared to obtain soils in a wide range of plasticity indices. Swell pressures

were directly measured from the constant volume swell tests performed on statically compacted

specimens with varying properties. The dependence of the swell pressure on the soil properties,

namely, initial water content, initial dry density and plasticity index was examined. Swell pressure

was correlated to the soil properties, using multiple regression analyses. The analyses haveconfirmed the existence of strong correlations between the swell pressure and the soil properties.

The correlations revealed a simple regression equation for a quick prediction of swell pressures

from easily determined soil properties.

In order to obtain clays possessing a wide range of plasticity index commercially processed

kaolinite and bentonite mineral clays were mixed in preselected proportions. The composition and

the consistency limits of the five clay mixtures are shown in Table 1.

Table 1. The composition and the consistency limits of the five clay mixtures used

Clay mixturetype

Kaolinite% by weight

Bentonite% by weight

LL (wL)

(%)

PL (wP)

(%)

PI(Ip)

(%)

1 95.24 4.76 50 20 30

2 90.91 9.09 70 20 50

3 86.96 13.04 88 20 68

4 83.33 16.67 105 21 84

5 80.00 20.00 118 21 87

LL orwL: liquid limit, PL orwP: plastic limit, PIorIp: plasticity index

Editor's note: This paper uses the old metric system unit of kg/cm2 which is equal to

approximately 100 kPa in SI (the use of kg, the mass unit, as if it were a force, is unacceptable in

SI).

Standard constant volume swell tests (ASTM D-4546) were performed on statically compacted

samples of the clay mixtures with intial water contents of 10, 15, 20, and 25% and having initial dry

densities of 1.5, 1.6, 1.7, and 1.8 g/cm3 in conventional oedometer cells; and the swell pressures of

each specimen, possessing plasticity indices, initial water contents and initial dry densities, weredirectly measured.

The dependence of the swell pressure on both the initial dry density and the plasticity index is

shown in Fig. 1 for samples at an intial water content of 15%. The data trends were similar for the


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entire range of initial water contents covered, indicating that an increase in the plasticity index or an

increase in the initial dry density results in a higher swell pressure value for samples having the

same initial water content. Similar results were observed by El-Sohby and El-Sayed (1981) and

Erol and Dhowian (1990).

Figure 1. The dependence of the swell pressure on the initial dry density

and the plasticity index for samples at an intial water content of 15%.

The relationship between initial water content and swell pressure is shown in Fig. 2 for the clay

mixture with plasticity index of 84. The figure shows that the initial water content has a small or no

effect on the swell pressure for samples at an initial water content less than the plastic limit, which

is 20 for the clay mixture in the figure. The figure also shows that for samples at an initial water

content at or above the plastic limit the swell pressure decreased with an increase in the water

content. The data trends were similar for the entire range of plasticity indices covered.

Figure 2. The relationship between initial water content and

swell pressure for the clay mixture with plasticity index of 84.


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The multiple regression analyses were carried out to correlate the logarithm of the measured swell

pressures to the soil properties, namely, initial water content and initial dry density, and revealed

the results as shown in Table 2. In equations 1 to 5 in Table 2, PS is the swell pressure in kg/cm 2;

rdry is the initial dry density in g/cm3; w is the initial water content in %; R is the coefficient of

multiple determination; and Std. Dev. is the standard deviation. The same units and symbols will be

used in subsequent analysis.These analyses with high coefficients of multiple determination confirmthe existence of strong correlations between the logarithm swell pressure and the soil properties IP,

w and rdry.

Table 2. Equations obtained from the correlation of swell pressures

to the initial dry density and the initial water content.

PIorIp (%) Equation R (%) Std. Dev. (%) Equation no.

30 log Ps = -5.424 + 3.084 rdry - 0.0247 w 85.3 15.6 1

50 log Ps = -4.785 + 2.862 rdry - 0.0215 w 91.6 11.4 2

68 log Ps = -3.689 + 2.310 rdry - 0.0150 w 96.0 6.1 3

84 log Ps = -3.083 + 2.033 rdry - 0.0128 w 98.1 3.7 4

97 log Ps = -2.681 + 1.853 rdry - 0.0117 w 98.8 2.7 5

As the values of the initial water content exceed the plastic limit its influence on the swell pressure

is significant, as mentioned before. The liquidity index (IL) combines consistency limits and the

in-situ moisture content of the soil (Lambe and Whitman, 1969). So, the liquidity index value of

each specimen was calculated. Then, the dependence of the swell pressure on the soil properties IL

and rdry was investigated. The multiple regression analyses carried out to correlate the logarithm of

the swell pressures to the two soil properties IL and rdry revealed the results as shown in Table 3.These analyses with high coefficients of multiple determination confirm the existence of strong

correlations between the logarithm swell pressure and the soil propertiesIP,IL and rdry.

Table 3. Equations obtained from the correlation of swell pressures

to the initial dry density and the liquidity index.

PIorIP (%) Equation R (%) Std. Dev. (%) Equation no.

30 log Ps = -5.914 + 3.082 rdry - 0.736IL 85.2 15.7 6

50 log Ps = -5.210 + 2.859 rdry - 1.077IL 91.4 11.5 7

68 log Ps = -3.995 + 2.315 rdry - 0.989IL 95.7 6.3 8

84 log Ps = -3.357 + 2.037 rdry - 1.072IL 98.0 3.8 9

97 log Ps = -2.929 + 1.854 rdry -1.116IL 98.6 2.8 10

Combined analyses including the entire range of the plasticity indices revealed the following

correlations:

log Ps

= - 4.812 + 0.01405 PI+ 2.394 rdry

- 0.0163 wi R2 = 94.1%

Std.Dev. = 10.9% (11)

log Ps = -5.197 + 0.01457 PI+ 2.408 rdry - 0.819IL R2 = 93.8% Std. Dev. (12)


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= 11.2%

These results with high coefficients of multiple determination confirm the existence of strong

correlations between the logarithm swell pressure and the soil properties. The swell pressures

obtained from Equation 11 are compared with the measured swell pressures in Fig. 3. The data

trends in the figure indicates that there is a good agreement between the measured and predicted

swell pressures.

In addition, the dependence of the swell pressure on two soil properties, namely, plasticity indexand initial dry density, was investigated. The multiple regression analyses carried out to correlate

the logarith of the swell pressures to the two soil properties IP and rdry revealed the following

equation:

log Ps = -5.020 + 0.01383 PI+ 2.356 rdry R2 = 89.6% Std. Dev. = 14.4% (13)

Equations 11, 12 and 13 reveal high coefficients of multiple correlation ofR2 = 94.1%,R2 = 93.8%

andR2 = 89.6%, respectively, indicating strong correlations between the swell pressure and soil

properties. However, Equations 11 and 12 has three soil properties while Equation 13 has two soil

properties. So, it is expected that the swell pressure of a clayey soil could be predicted usingEquation 13 from easily determined soil properties, namely, plasticity index and initial dry density.

Figure 3. Comparison of measured/predicted swell pressures.

The data trends and the statistical analysis presented throught the study reveals the following:

1. The swell pressure is strongly dependent on initial dry density and plasticity index, but less

affected by initial water content.

2. Significant correlations exist between the swell pressure and the soil properties, and revealed a

simple regression equation for a quick prediction of swell pressures from easily determined soil

properties.


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Al-Mhaidip, A., 1999. Swelling behavior of expansive shales from the middle region of

Saudi Arabia. Geotechnical and Geological Engineering, Vol. 16, pp. 291-307.

1.

ASTM, 1990. Test methods for one-dimensional swell or settlement potential of cohesive

soils. ASTM Method D.

2.

Azam, S. and S.N. Abduljauwad, 2000. Influence of gypsification on engineering behavior of

expansive clay. Journal of Geotechnical and Geoenvironmental Engineering, Vol.126, No. 6,

pp. 538-542.

3.

Dhowian A., Orhan Erol, and Abdulfattah, Y., 1988. Evaluation of expansive soils and

foundation methodology in the kingdom of Saudi Arabia, King Abdulaziz City for Science

and Technology, Riyad.

4.

El- Sohby, M.A. and A. R. El-Sayed, 1981. Some factors affecting swelling of clayey soils.

Geotechnical Engineering, Vol. 12, pp. 19-39.

5.

El- Sohby, M.A. and A. R. El-Sayed, 1983. Mineralogy and swelling of expansive clayey

soils. Geotechnical Engineering, Vol. 14, pp. 79-87.

6.

Erol, O. and A. Dhowian, 1990. Swell behavior of arid climate shales from Saudi Arabia,

QJEG, Vol.23, pp. 243-254.

7.

Komornik, A. and D. David, 1969. Prediction of swelling pressure of clays. Journal of

SMFE Div., ASCE, Vol. 95, No. SM1, pp. 209-225.

8.

Lambe, T.W. and R.W. Whitman, 1969. Soil Mechanics.John Wiley and Sons, Inc., N.Y.9.

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