Mechanical Properties of Limestone Under Different Confining Pressures and Wet–Dry Cycles

During the operation of large reservoirs, slope rock masses at different elevations are subjected to confining pressure variation and alternating wet–dry cycles induced by water-level fluctuations, resulting in the evolution of their mechanical properties. To investigate this issue, conventional triaxial compression tests were conducted on limestone from Badong County in the Three Gorges Reservoir area under confining pressures of 5–20 MPa and 0–50 wet–dry cycles. The results show that confining pressure significantly enhances limestone strength, whereas wet–dry cycles induce a progressive deterioration in mechanical properties. Under the same confining pressure, the deterioration exhibits a staged characteristic, with a rapid decrease at the early stage followed by a slower decline. Higher confining pressure effectively suppresses crack propagation and mitigates the degradation caused by wet–dry cycling. Meanwhile, wet–dry cycles promote the transition of the failure mode from single-fracture failure to multi-fracture fragmentation. The elastic modulus, cohesion, and internal friction angle all decrease exponentially with increasing wet–dry cycles. Based on damage mechanics theory, a constitutive relationship considering wet–dry cycle effects was established to characterize rock stiffness degradation and its influence on the overall mechanical response. The proposed model effectively describes the evolution of mechanical parameters and deformation characteristics under wet–dry cycling conditions. This study provides an experimental and theoretical basis for evaluating the long-term stability of reservoir slopes.