Influence of Intermediate Principal Stress on Shear Strength of Natural Granite Residual Soil

Abstract

As a result of weathering, the mechanical behavior of granite residual soil differs from that of sedimentary soil. Although the mechanical properties of granite residual soil have been studied extensively, its strength anisotropy is yet to be established. Previous work has revealed the association between the principal stress direction α and soil shear strength, but little is known about how the intermediate principal stress affects the soil strength. This paper presents the shear-strength parameters under various combinations of α and the intermediate principal stress factor b as obtained through undrained hollow-cylinder torsional shear tests performed on samples of natural granite residual soil. The test results confirmed the considerable effect of b on the shear strength and highlighted the differences between the soil studied here and those studied previously. It was found that b affects the undrained strength and mobilized frictional angle (or ultimate stress ratio) differently, with increasing b leading to lower undrained strength but higher frictional angle. In addition, the degrees to which b affects undrained strength and frictional angle are not the same and depend on the α value at which the soil is sheared. Therefore, two parameters are proposed to quantify that difference. This study extends the understanding of the strength anisotropy of granite residual soil and provides data for soil behavior under various values of b.