Research on the Macro‐Micro Energy Evolution Law and Segmented Damage Constitutive Model of Sandstone Under Dry‐Wet Cycles

ABSTRACT The periodic fluctuation of reservoir water levels induces dry‐wet cycles, deteriorating sandy rock slope stability and potentially triggering collapses. This study investigates the degradation mechanism of Three Gorges Reservoir fine sandstone through uniaxial compression tests and PFC2D simulations under varying dry‐wet cycles. Key findings include: (1) Increasing cycles reduce uniaxial compressive strength and elastic modulus (showing “V‐shaped” and “N‐shaped” degradation trends), while permeability and porosity rise, and P‐wave velocity declines. (2) Crack growth is nonlinear, dominated by shear cracks and high‐angle microcracks, with force chains aligning with the loading direction. (3) Dissipation energy rate follows a “W‐shaped” trend, while elastic energy rate exhibits an “M‐shaped” pattern; both energies at crack initiation, damage, and peak stress correlate exponentially with cycle count ( K sd being more sensitive). (4) Dry‐wet cycles weaken intergranular bonds, reduce elastic energy storage ( U e ), increase dissipated energy ( U d ), lower M ‐value stability, and shift failure from brittle to ductile. (5) A Weibull‐based segmented damage model effectively simulates sandstone behavior under cyclic conditions. These insights enhance understanding of reservoir slope stability under hydrological fluctuations.