The influence of fracture mechanisms on the evolution of strain energy in sandstone under various stress states

Deep rocks are subjected to true triaxial stress conditions, where their deformation and failure characteristics are determined by the stress state. In order to study the failure modes and energy evolution laws of sandstone under different stress states, this study conducted loading tests on sandstone under different minimum principal stresses and monitored its acoustic emission signals. The stress-strain relationship and energy evolution laws of sandstone were analyzed, and the influence laws of sandstone fracture mechanism on the types of strain energy and its evolution were discussed. The results show that as the minimum principal stress increases, the peak strength and residual strength of sandstone increase, and the total strain energy, elastic energy and dissipated energy before failure also increase, of which the proportion of dissipated energy increases accordingly. By calculating and plotting the relationship curves between the ratio of rise time to amplitude (RA value) and the ratio of count to duration (AF value) in acoustic emission waveforms, and by observing fracture morphology, it was found that sandstone exhibits tensile-shear composite failure under lower minimum principal stress, while the failure mode gradually shifts to shear-dominated with increasing minimum principal stress. Throughout the entire loading and failure process of sandstone, the dissipated energy and plastic shear strain energy curve show a positive correlation. Before failure, the curve transforms from nonlinear to linear with the increase of minimum principal stress, indicating that plastic shear strain energy gradually dominates energy dissipation. After failure, the curve grows linearly, which may be attributed to the fact that energy dissipation is primarily caused by slip friction along macroscopic failure surfaces. The research results reveal the energy evolution mechanism of deep-seated dynamic disasters and provide a theoretical basis for disaster early warning and prevention and control.