Experimental Study On Hydraulic Coupling Triaxial Test Of Sandstone Under Cyclic Loading

High stress and High osmotic pressure were occurred in deep underground engineering.The deep surrounding sandstone sustain addition stress caused by excavation.It will also be subjected to repeated blasting,mechanical sandstone drilling and even mineral earthquakes in subsequent excavation construction.Combined with high osmotic pressure,it will have an important influence on the deformation of the sandstone,as well as the damage evolution and rupture process.To study the stress-strain relationship and permeability change of sandstone under cyclic loading in hydraulic coupling environment.Conventional triaxial tests,orthogonal test of conventional hydraulic coupled test and cyclic load hydraulic coupled test are set.On this basis,the hydraulic coupling test of equal amplitude cyclic loading was added.Based on the test results,the mechanical properties,deformation characteristics and permeability of sandstone under cyclic loading in hydraulic coupling environment are systematically analyzed.The main research results include:Mechanical properties: under the condition of mechanical coupling,the peak strength of sandstone increases with the increase of confining pressure or the decrease of osmotic pressure under conventional hydraulic coupled triaxial test.However,under cyclic loading,the change variation of peak strength of sandstone is greater.The cyclic loading makes the sandstone fall faster after reaching the peak strength.The brittleness of sandstone was be shown,but with the increase of osmotic pressure,the degree of sharpness gradually decreases,and the brittleness of sandstone turns to plastic characteristics,ultimately achieves stable residual strength.Permeability: With the increase of confining pressure and the decrease of osmotic pressure,the permeability of sandstone presents a growth mode under conventional hydraulic coupled triaxial test.The failure mode of sandstone is single splitting failure.Under cyclic loading,the change of permeability of sandstone after dilatation stage is different from that under conventional loading.The failure mode of sandstone is a mixed failure mode of multi-angle and multi-crack.Sandstone failure mode affects the change of permeability.It is fundamentally related to the tortuosityand the process of sandstone failure.A fatigue damage model of sandstone under variable amplitude cyclic loading and hydraulic coupling is established.It is verified with the permeability measured by the test and the accuracy of fitting is higher.During the last cycle,the permeability of sandstone varies most with confining pressure.The exponential power of the fitting curve decreases with the increase of confining pressure.