Shear Strength of Earth Materials in a Weathering Profile Over Granite

Abstract

The weathering profile can be separated into an upper, 11.8 m thick pedological soil (zone I) comprising gravelly clayey sands and a lower, 31.9 m thick saprock (zone II) of silty gravelly sands that distinctly preserve the minerals, textures and structures of the original granite. Consolidated drained triaxial tests on five sets of undisturbed samples from sub-zones IC2 (set A), IIB (set B), IIC (set C) and IID (sets D and E) yield effective cohesions (c') of 34.4 kPa, 22.7 kPa, 24.7 kPa, 27.2 kPa, and 14.5 kPa, and friction angles (φ') of 30.7°, 33.5°, 31.5°, 32.5°, and 34.4°, respectively. Regression analyses show the effective cohesion of samples from sub-zones IIC and IID to decrease with increasing moisture contents retained at 33 kPa, and 1,500 kPa, suction pressures; features indicating the decreasing influence of capillary and sorptive forces, respectively.