Case Study on the Failure Characteristics and Energy Evolution of Three Types of Hole-Fissured Sandstone Under Wetting–Drying Cycles

Engineering structures, including rock slopes and embankments, are vulnerable to wetting–drying cycles caused by tidal shifts and rainfall, which exacerbate mechanical degradation in hole-fissured sandstone. This study investigated the effects of 0, 10, and 20 wetting–drying cycles on sandstone samples using uniaxial compression tests combined with digital image correlation (DIC), computed tomography (CT), and scanning electron microscopy (SEM). The results revealed that wetting–drying cycles progressively reduced peak strength and the elastic modulus while increasing macroscopic crack quantity and width. Internal crack networks simplified, transitioning from tensile-dominated to combined tensile–shear and shear failure modes. An energy analysis showed diminished energy storage capacity—both the total energy density at peak stress and elastic strain energy density declined with increasing cycle numbers, whereas dissipated energy density decreased initially before rising. SEM observations indicated that wetting–drying cycles enhanced the surface roughness of the sandstone, characterized by a scaly texture, thereby compromising its structural integrity. This study provides a theoretical basis for stability and safety assessments of protective engineering systems.