Mechanical Properties And Energy Evolution Law Of Sandstone Under Hydro-mechanical Coupling

Deep underground engineering is often affected by groundwater pressure,resulting in instability and failure of surrounding rock.The hydro-mechanical coupling characteristics of rock has always been a hot issue in the field of mine project.In this paper,sandstone is taken as the research object,and a series of conventional mechanical tests and triaxial compression tests under hydro-mechanical coupling were carried out.The relationship between rock mechanical property parameters and pore water pressure is analyzed,and a generalized strength reduction criterion for rock under hydro-mechanical coupling is established based on the regularity of rock strength reduction.In addition,combined with the total stress-strain curve and effective strength concept of water-saturated sandstone under the action of hydro-mechanical coupling,the energy value of the rock full stress process was calculated by the micro-element method,and the effect of pore water pressure on the dissipated energy and elastic energy of the saturated sandstone specimen was analyzed.The main research contents are as follows.(1)The Brazilian splitting,uniaxial compression and conventional triaxial compression tests were carried out on dry sandstone and water-saturated sandstone,and the basic mechanical parameters of the sandstone were obtained.It was found that the tensile strength,compressive strength and triaxial compressive strength of water-saturated sandstone are lower than those of dry sandstone.and the strength of sandstone under triaxial compression increases with the increase of confining pressure.The failure modes of dry sandstone and water-saturated sandstone are not much different,and they are X-shaped conjugate shear failure and single-inclined shear failure under uniaxial and triaxial compression respectively.(2)The triaxial compression test under hydro-mechanical coupling was carried out on the water-saturated sandstone,and the whole stress-strain curve and related mechanical parameters of the water-saturated sandstone were obtained.It was found that under the same confining pressure,the peak deviatoric stress,residual deviatoric stress,initial deviatoric stress of expansion,peak axial strain and modulus of deformation of water-saturated sandstone decrease with the increase of pore water pressure.When the pore water pressure remains unchanged,the peak deviatoric stress,residual deviatoric stress,initial deviatoric stress of expansion,peak axial strain and modulus of deformation of the specimen increase with the increase of the confining pressure,and the Poisson’s ratio increases with the increase of the confining pressure.(3)Based on the principle of effective stress,the expressions of M-C criterion,D-P criterion,SMP criterion and H-B criterion for the peak strength and residual strength of water-saturated sandstone under hydro-mechanical coupling were obtained.And the relationship between the initial stress of expansion of water-saturated sandstone,confining pressure and pore water pressure.According to the phenomenon of rock strength reduction under pore water pressure,a generalized strength reduction model for rock under hydro-mechanical coupling was established.And further proved that the strength model has high reliability and universality.(4)The energy values of the water-saturated sandstone during the total stress-strain process under hydro-mechanical coupling was calculated by the micro-element method.It was found that the dissipated energy increases with the increase of the axial strain,and the variation trend of the elastic energy is consistent with the stress-axial strain curve of sandstone.The peak dissipated energy and elastic energy of water-saturated sandstone have a linear negative correlation with the pore water pressure.The change value of the dissipated energy and elastic energy of the water-saturated sandstone at failure time are positively correlated with the confining pressure.