Study On Mechanical Properties Of Saturated Sandstone After Peak Cyclic Loading And Unloading Under Hydro Mechanical Coupling

Deep underground rock roadway is often damaged by the influence of groundwater and in-situ stress.In the process of repairing the damaged rock roadway,the rock roadway is in a state of cyclic loading.In order to better guide the roadway repair work in the environment with groundwater,this paper carried out the mechanical characteristics test of saturated sandstone after peak cyclic loading and unloading under water force coupling.Taking the saturated sandstone as the research object,the conventional triaxial mechanical test of saturated sandstone was carried out by MTS815 mechanical testing machine,and the cyclic loading and unloading after peak under the combined action of water pressure and confining pressure The main research contents are as follows（1）The basic mechanical parameters of saturated sandstone are obtained by conventional triaxial tests.It is found that with the increase of confining pressure,the specimen changes from elastic brittleness to elastic plasticity.Under the condition of triaxial compression,the specimen is single inclined plane shear failure.The fracture angle increases with the increase of confining pressure.（2）The cyclic loading and unloading experiments of saturated sandstone under different water pressures and confining pressures are carried out,and the loading modulus and unloading modulus of saturated sandstone are obtained.Through the analysis of the experimental results,it is found that the weakening effect of water pressure on the residual strength of the specimen is greater than that on the maximum peak stress of the specimen,and the enhancement effect of confining pressure on the residual strength of the specimen is greater than that on the maximum peak stress of the specimen.Under the same confining pressure,the maximum peak stress and residual strength of saturated sandstone specimens are negatively correlated with water pressure;under the same water pressure,the maximum peak stress and residual strength of saturated sandstone specimens are negatively correlated with confining pressure.（3）The energy analysis and damage analysis of saturated sandstone under post peak cyclic loading and unloading show that the proportion of dissipated energy in the total cyclic energy of the specimen decreases with the increase of water pressure under the same confining pressure when the specimen reaches the residual state.Under the same water pressure,the proportion of dissipated energy in the total cycle energy increases with the increase of confining pressure.Compared with the dissipative energy method,the elastic modulus method can better analyze the full stress-strain curve of water saturated sandstone under water pressure.