Compression and Shear Strength Characteristics of Unsaturated Intact Loess in True Triaxial Tests

Previous studies of shear behavior from suction-controlled direct shear tests or triaxial tests focused mainly on remolded soils. Limited attention has been paid to suction measuring on unsaturated intact soil. In this paper, two series of saturated drained tests and unsaturated constant water content (CW) tests containing isotropic consolidation and shear tests with different intermediate principal stress parameters b were conducted to investigate deformation and shear strength characteristics of intact loess using unsaturated true triaxial apparatus. The initial suction decreases with an increase in initial degree of saturation. The void ratio decreases with an increase in suction and net mean stress. The isotropic compression yield stress increases as initial suction increases. The suction after isotropic consolidation is less than the initial suction. The shear strength increases with an increase in b-value, net confining pressure, and suction. The failure state line on the effective stress p’–q’ plane of Schrefler is approximately a straight line passing the origin at different intermediate principal stresses. The effective stress–strength failure surfaces on the π plane are similar in shape and can be approximated by the spatially mobilized plane (SMP) strength criterion. When the initial suction is constant, the cohesion increases with an increase in b-value and increases linearly with an increase in initial suction at different b-values. The influence of initial suction (i.e., water content) on the internal friction angle is very small, and the internal friction angle decreases linearly with an increase in b-value. There is a nonlinear phenomenon between shear strength and suction. The equation expressions of cohesion, initial suction, and b-value, and internal friction angle and b-value are obtained.