Experimental Study on Strength and Failure Characteristics of Jinping Marble under Loading and Unloading Stress Paths

Large-scale hydropower projects in Southwest China face severe challenges due to complex geological environments and the presence of steep rock slopes. Ensuring long-term slope stability is essential for the safety of such projects. This study investigates the deformation, strength, and failure characteristics of Jinping marble under dry and saturated conditions through conventional triaxial compression and stress-path-controlled loading-unloading tests. Results show that confining pressure governs the failure mode: brittle axial splitting and sudden stress drops occur at low pressures, while ductile deformation with shear failure develops at higher pressures. Water saturation significantly weakens mechanical properties, reducing peak strength by an average of 10.8% and decreasing elastic modulus, with larger differences at lower confining pressures. Stress path analysis demonstrates that unloading increases the failure approach rate. Notably, when the unloading rate is set to 0.2 times the axial loading rate, the strength under unloading becomes nearly identical to that under conventional loading, indicating that stress path has little effect near peak strength for brittle marble. These findings emphasize the coupled roles of confining pressure, water saturation, and stress path in rock behavior, providing valuable insights for constitutive modeling and the long-term stability evaluation of high rock slopes in hydropower engineering.