Macro- and Micromechanical Behaviors and Energy Variation of Sandstone under Different Unloading Stress Paths with DEM

Abstract

Various mechanical responses of rocks under a complex stress state have attracted the attention of engineers. A hollow cylinder torsional apparatus (HCA) was constructed using the discrete element method (DEM). A series of conventional triaxial compression tests under different confining pressures and a complex stress path test with torsion were conducted. The numerical results are consistent with laboratory and theoretical findings, which indicates that the microscopic parameters of the DEM sandstone specimens were correct and reasonable. Based on the HCA DEM specimen, the macro–micromechanical response of sandstone specimens under four typical unloading stress paths were studied, and variations in the strain energy density, strain energy, and dissipated energy of sandstone specimens were obtained. These results could provide a reference for the study of the mechanical properties of unloaded sandstone in geotechnical engineering.