Investigation of hydro-mechanical coupling characteristics of stress-induced anisotropic unsaturated clay

Lots of geotechnical engineering problems are closely related to the anisotropic behavior of unsaturated clay. In this paper, suction-controlled, consolidated, drained triaxial shear tests were conducted on clay under unsaturated conditions. For unsaturated clay, the effects of matric suction, initial stress ratio, and subsequent stress ratio on the hydro-mechanical coupling characteristics were studied, and the evolution of water retention, stress-induced anisotropy characteristics and critical state parameters under different stress paths were obtained. The stress path significantly influences the water retention capacity of clay, with the initial stress ratio identified as a pivotal determinant of the air entry value. The shear strength, stress–strain behavior, and volumetric characteristics of unsaturated clay are jointly influenced by initial stress ratio, subsequent stress ratio, and matric suction. Increasing subsequent stress ratio generally decreases shear strength and enhances strain softening, while higher matric suction improves shear strength and promotes dilatancy. In the p * – q plane, a unique critical state line ( q = M * p * ) exists, independent of matric suction and stress paths. In the ln p * – v plane, critical state lines at different matric suctions are parallel.