Tensile failure and ductile-to-brittle transition of sandstone under three-dimensional seepage pressureOA

After reservoir impoundment,fractures and pores in the rock mass serve as important pathways for seepage,and the resulting fluid pressure can easily trigger engineering issues such as slope instability and dam deformation.To investigate the mechanical properties and failure characteristics of sandstone under hydro-mechanical coupling,triaxial compression tests were conducted under various confining pressures.Combined with acoustic emission monitoring and numerical simulations,this study revealed the internal failure mechanisms and mechanical responses of sandstone in its natural state,after soaking,and under seepage pressure.The experimental results indicate that:(1)with increasing confining pressure,the failure mode of natural and soaked sandstone samples transitions from brittle to ductile,whereas under seepage pressure the failure mode shifts from ductile to brittle;(2)natural sandstone predominantly fails by shear,while soaked sandstone exhibits a mixed failure mode dominated by shear,and under seepage pressure,the samples display a mixed failure mode dominated by splitting;(3)as confining pressure increases,crack propagation is suppressed,leading to a transition from tension-dominated to shear-dominated failure;soaking facilitates stable crack propagation,thereby delaying ultimate failure and exhibiting significant ductile characteristics,whereas seepage pressure accelerates crack development,significantly reducing rock strength and markedly enhancing brittle failure characteristics.