Experimental study and predictive analysis of contribution of matrix suction to shear strength of weak expansive soil

Several formulas for predicting the shear strength of unsaturated soils by the soil-water characteristic curve (SWCC) are summarized and discussed. The SWCC and unsaturated shear strength parameters of intact weak expansive soil from Jingmen City, Hubei Province are measured by the pressure plate and unsaturated triaxial apparatus; based on the comparison of the test results with the predictive values of the several shear strength formulas, the limitations of the formulas are analyzed. The results show that the friction angle of the net normal stress varies with the change of matrix suction for the unsaturated intact expansive soil. According to the double stress variables theory, the contribution of matrix suction to the shear strength of unsaturated expansive soil is associated with cell pressure and different in different cell pressure levels; it is suitable that the variable characteristic of the apparent cohesion us. with suction is described by power function.