The Variation of Total Volume Change, Water Volume Change, Yielding Net Confining Stress and Shear Strength of Undisturbed Unsaturated Loess under Isotropic Compression

Abstract

Catastrophic failures in residential building foundations due to wetting collapse is a very serious problem in loessial arid zones. In this research, the variation of total volume change, water volume change, yielding net confining pressure and shear strength of undisturbed unsaturated loessial soil samples obtained from an arid zone in Golestan province in Iran, is studied by manipulating a full stress path controlled unsaturated triaxial apparatus at Sharif University of Technology. For this purpose, isotropic compression tests were performed on the specimens for five different values of constant matric suction while raising the net confining pressures in wetting path. Also at the end of isotropic compression tests, deviator stress was applied to obtain the shear strength parameters of the soil. Results show that for different values of matric suctions the values of total volume changes, water volume changes and yielding net confining pressures vary significantly and the shear failure envelope supports the extended Mohr-Coulomb theory for unsaturated soils.