Damage evolution and microscopic failure characteristics of dense sandstone at different water contents

To reveal the mechanical degradation, damage evolution, and failure mechanism of dense sandstone under varying water content, uniaxial compression tests were conducted on sandstone with different water contents. Combined with acoustic emission monitoring, scanning electron microscopy, and energy evolution analysis, constitutive models of damage evolution in sandstone with different water contents were established. The deformation and failure characteristics of water-bearing sandstone were systematically studied at both macroscopic and microscopic scales. The results show that with increasing water content, the peak strain, compressive strength, and elastic modulus of sandstone generally decrease, and the degradation pattern is initially steep and then gradual. Increasing water content gradually lowers the damage threshold of sandstone, leading to earlier damage evolution. The cumulative acoustic emission count and cumulative energy decrease overall, and moisture has a significant inhibitory effect on crack propagation and energy release. In terms of failure mode, sandstone gradually shifts from shear failure to tensile failure, with the proportion of tensile cracks increasing significantly with increasing water content. Microscopically, the fracture morphology gradually transforms from relatively smooth transgranular fractures in the dry state to rougher intergranular fractures and coupling fractures. These findings can provide a theoretical basis for the analysis of the mechanical properties of deep water-bearing dense sandstone surrounding rocks and their engineering applications.