Stress probing analysis of recent stress history effects on small-to-medium strain stiffness of granular materials

This paper investigates the effects of recent stress history (RSH), specifically sudden changes in the stress path direction, on the small-strain stiffness and stiffness degradation characteristics of granular materials, using three-dimensional discrete element method (DEM) simulations. Specimens with varying RSHs are prepared via a series of approach paths from diverse directions, involving deviations from and returns to a common stress state. The norm of the induced plastic strain, obtained through a stress probing technique, is proposed as a criterion to determine the extent of the approach path. Subsequently, constant-p triaxial compression tests are conducted to analyze the effects of different RSHs on stress–strain response, small-strain stiffness, and stiffness degradation. Results reveal that specimens experiencing full stress reversal exhibit significantly higher small-strain shear stiffness than those under sustained load directions. Specimens loaded with counterclockwise stress rotation angles exhibited slightly greater stiffness than those with equivalent clockwise angles. Furthermore, the configuration of stiffness degradation curves, defined by onset and reference shear strain, is strongly influenced by the stress rotation angle. Stress probing reveals that RSH mainly affects total shear stiffness degradation by altering the extent of plasticity, with the elastic stiffness remaining largely unaffected. Finally, a modification to an existing stiffness model is proposed by introducing an RSH-dependent factor, complementing the effects of void ratio, stress state, and shear strain, to enhance predictive accuracy.