Hydro-mechanical damage modeling of water-bearing sandstone using an energy dissipation approach under triaxial stress

Deep mining in water-rich strata subjects roadway surrounding rock to complex water–rock interactions, leading to severe nonlinear deformation and instability. To investigate the influence of groundwater on rock mechanics, this study employed triaxial compression tests ( σ z = 20 MPa, σ x = σ y = 15 MPa) on sandstone specimens from the Yingping Section of the Wengfu Phosphate Mine, Guizhou Province. Specimens with varying moisture contents (0% dry, 0.52%, 2.56%, 5.01%, 7.33% saturated) were prepared using a solution simulating local groundwater chemistry. Results show that increasing moisture content significantly degrades mechanical properties: peak strength nonlinearly decreased from 142.9 MPa (dry) to 89.21 MPa (saturated), exhibiting a two-stage attenuation pattern with a higher rate (8.32 MPa/%) below a critical moisture content of 5.01% and a lower rate (5.18 MPa/%) above it. Elastic modulus decreased by 68.07% (37.02–11.82 GPa) while Poisson’s ratio increased from 0.18 to 0.33. Energy analysis revealed prolonged deformation accumulates more total energy, reduced elastic strain energy storage efficiency, and inhibited dissipated energy growth due to water lubrication. Based on energy dissipation, a hydro-mechanical coupled damage constitutive model incorporating both water-induced and mechanically induced damage was developed and validated against experimental stress–strain data, showing strong agreement, particularly pre-peak. These findings provide theoretical support for stability control in deep water-rich roadways.