Triaxial compression tests of QH-E lunar soil simulant under constant mean principal stress path using discrete element method simulations

In this paper, discrete element method (DEM) simulations are applied to investigate the triaxial compression tests of QH-E lunar soil simulant (developed by Tsinghua University, China) under constant mean principal (P) stress path. The P stress path is achieved by controlling the loading speed and direction of the axial stress and confining stress in the DEM simulations, the strain softening and dilatancy characteristics of QH-E lunar soil simulant both at low and conventional P stress levels are discussed. The results show that the deviatoric stress–strain curve is divided into hardening, softening descending, and residual strain stages, and the shear strength and residual strength increase with the increase of P stress, which are similar to the conventional triaxial compression tests. The volumetric strain versus shear strain curve shows a good linear relationship both at the linear shear dilatancy and residual shear dilatancy stages, but the slope of the linear dilatancy stage is larger than that of the residual dilatancy stage. Furthermore, it is found that the variations of shear dilatancy characteristic parameters with regard to P stress also show a good linear relationship, and the values of these parameters increase with the increase of P stress.