Experimental Study on Strength and Non-Coaxiality of Sand under Fixed Principal Stress Axes Shearing

Given the problem that most of the existing shear tests with fixed principal stress direction ignore the change of intermediate principal stress coefficient b. The loading parameters of the four external loads of the hollow cylindrical apparatus were strictly deduced based on the mapping relationship between different force systems. The shear tests with fixed principal stress direction were carried out under two groups of confining pressures using remodeled Fujian standard sand specimens. The differences in mechanical properties such as deformation, strength, and non-coaxiality of the sand were studied when the principal stress direction α was different. Test results show that the stress path, strength, and other mechanical properties of sand have a significant stress direction dependence. With the principal stress direction changes from 0° to 90°, the stress path shows two variable phases, the peak strength decreases and then increases, and the minimum value of strength near α of 67.5°. The specimen has an obvious non-coaxiality when the deviatoric stress ratio is small, according to a comparison of the major principal strain increment direction and the major principal stress direction. However, as the deviatoric stress ratio increases, the direction of the principal strain increment gradually approaches the principal stress direction.