Influence of Complex Stress Path on Energy Characteristics of Sandstones under Triaxial Cyclic Unloading Conditions

This paper explores the characteristics of energy accumulation, evolution, and dissipation of sandstone samples under different confining pressure conditions in the triaxial cyclic unloading test. The characteristics of the stress-strain relationship of deformation and failure of rock samples are analyzed in detail. By utilizing the integral method for the area, the densities of total energy, elastic energy, and dissipated energy under different confining pressure are calculated. In addition, the energy evolution laws of rock deformation and failure with cyclic unloading times are researched. The results demonstrate that during the unloading cycle of confining pressure, the total energy density u, elastic energy density u(e), axial total energy density u(1), and axial elastic energy density u(e)(1) increase, the radial total energy density u(3) and the radial elastic energy density u(e)(3) decrease, and the dissipated energy density is almost unchanged. The total energy density u and elastic energy density u(e) of rock under different confining pressure cycle unloading have a significant linear relationship. Meanwhile, the scanning electron microscope image shows the microstructure characteristics of the cracks in the sandstone samples. The image results are consistent with the analysis of the macroscopic failure characteristics. Under the same stress path, the higher the initial confining pressure, the more severe the failure of the rock sample. The experimental results are expected to enhance the basic research on the energy characteristics under the triaxial unloading behavior of rock.