Experimental Verification of a Theoretical Model for Shear Strength   Omer Nawaf Maaitah Asistant Professor, Civil Engineering Department Faculty of Engineering, Mutah University, Karak, Jordan E-mail: abponkm@mutah.edu.jo
			ABSTRACT

An experimental program was designed to study the behavior of unsaturated soil at low degree of saturation and to verify theoretical models. Two types of test were performed on unsaturated soil. These tests include: (1) constant normal stress and many tests with different degrees of saturation, (2) constant degree of saturation and many tests with different normal stress. In both types of tests the air pressure was allowed to drain but water pressure was held in. Also many tests were conducted on unsaturated soil to show the effect of particle size. Tests carried out on fully saturated samples to determine the effective angle of friction.

It was found that as the degree of saturation increases from 2 % up to 40 % the shear strength increases and then it decreased as the saturation level increases. All the measured values of unsaturated shear strength have been compared with predicted values from the theoretical model that was suggested by Maaitah 2000. Predicted and measured values were in good agreement. Furthermore, it was found that there is no unique value for the ratio, (, and it is a function to soil type and to the degree of saturation.

It has been found that unsaturated critical state lines (CSL) are parallel to the saturated lines where the slope, M, is equal to 1.18 and independent of the saturation state. On contrast, the intercept, qo of the CSL for unsaturated soil on the (q: p ) plane as a function of saturation state.

Keywords: Degree of saturation, critical state, unsaturated soil, shear strength, predicted and measured strength

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