True Triaxial Test Study On Mechanical Properties Of Deep Rock Mass In Different Stress Paths

This article prepares cubic specimens from granite and sandstone.True triaxial loading and unloading tests under different confining pressures and true triaxial tests under different unloading paths are performed using true triaxial tests in the laboratory,theoretical analysis and numerical simulation,The mechanical characteristics of rocks under loading and unloading conditions and the deformation and failure laws of rocks under different unloading paths and the variation of mechanical parameters are compared and analyzed by experimental data.The research results and main contents of the dissertation are as follows:(1)The true triaxial loading and unloading tests of rock under different confining pressures show that under true triaxial compression the deformation of the rock specimen is manifested as axial compression and expansion along the direction of the minimum principal stress.The deformation of rock specimens under the true triaxial unloading condition is dominated by the unloading direction,and the brittleness characteristics of rock failure are more obvious.(2)Under true triaxial compression conditions,the deformation modulus of the granite specimen increases with increasing axial pressure before the peak axial pressure is reached,the deformation modulus of sandstone specimens will decrease as the axial pressure increases.Under true triaxial unloading conditions,the deformation modulus of the specimen increases with the increase of the initial confining pressure,decreases continuously during the unloading process,and the Poisson's ratio increases with decreasing stress on the unloading surface.(3)The true triaxial tests of granite and sandstone under different unloading paths have found that the failure of rock specimens is caused by the expansion along the unloading direction.The unloading load on the single side of the increasing axial pressure is the smallest,and the rock specimen deformation is the most severe.The unloading volume of rock specimens is the largest in the axial uniaxial unloading path,and the rock specimen destruction process is relatively slowest.The rock specimens all show the characteristics of composite failures of tensile and tensile shears,but the sandstone specimens are more fragmented than granite specimens under the same unloading path.(4)Under triaxial loading and unloading conditions,the bearing capacity of rock specimens increases with the confining pressure.In all three unloading paths,the ultimate bearing strength of rock specimens decreases with decreasing stress on the unloading surface.(5)Four kinds of widely used strength criterions were used to fit the rock failure stress data obtained under constant confining pressures of granite and sandstone under different confining pressures.The Mogi-Coulomb criterion can more accurately reflect true triaxial unloading loads.Rock strength characteristics under conditions.(6)The numerical simulation of rock unloading mechanical properties was performed using FLAC3D.It was found that during the unloading process,the shear strain rate in the model increased to form a shear band,and the shear bands interpenetrated eventually resulting in the formation of multiple shear cracks inside the model.The fracture surface of the fracture surface is fractured and destroyed near the unloading surface.Finally,the failure surface penetrates each other and the entire model is destroyed.