Analysis on pre-peak deformation and energy dissipation characteristics of sandstone under triaxial cyclic loading

Based on conventional triaxial cyclic loading-unloading compression tests, the axial and lateral elastic-plastic strains of sandstone under confining pressures of 5, 10, 20 and 30 MPa were analyzed. The results showed that the lateral stress-strain plastic hysteresis loop is more obvious than the axial direction under cyclic loading. The axial and lateral elastic strains of the specimens are nonlinearly related to the axial deviatoric stress, and the axial and lateral plastic strains of the specimens show obvious non-linear plastic hardening characteristics. The Duncan-Chang model is used to analyze the elastic stress-strain characteristics of sandstone during loading. Without considering the initial stage of fracture compaction, the tangent elastic modulus of the sandstone specimens decreases continuously with the increase of the axial elastic strain and the Poisson's ratio increases continuously with the increase of lateral elastic strain under the same confining pressure. Based on the plastic strain characteristics of sandstone specimens, the corresponding plastic flow equation is established, which can preferably describe the axial and lateral strain characteristics of the specimen. The plastic flow rate of the specimens increases nonlinearly with the increase of the axial deviatoric stress, which approaches the ideal plastic flow state near the peak strength.