Experimental investigation on progressive damage mechanical behavior of sandstone under true triaxial condition

Based on the idea of deep initial high in-situ stress state reduction,the true triaxial orthogonal mechanics tests of sandstone under different stress paths and simulated depths were conducted by using the multifunctional true triaxial fluid-solid coupling test system. The stress-strain curves of sandstone under different true triaxial working con-ditions were obtained during the entire deformation process. The Z,Y and X direction progressive damage evolution laws of sandstone were analyzed. The progressive damage mechanical behavior evolution characteristics of sandstone under the true triaxial condition were characterized,which could better reflect the progressive deformation and failure mechanism of surrounding rock after excavation at deep mine roadway. The results show that the peak strength of sandstone increases with the increase of the simulation depth under different simulated depths and same stress path,which shows that the deep effect is significant for the strength evolution law of sandstone. The Z direction principal strain of sandstone increases with the increase of the Z direction principal stress under different stress paths and the same simu-lation depth,but the X direction principal strain decreases with the increase of the Z direction principal stress,which shows that the stress loading path is a major effected factor for the progressive deformation and failure mechanism of sandstone in X and Z directions. The Y direction principal strain of sandstone increases with the increase of the simula-tion depth under path 2 and path 3,while the Y direction principal strain of sandstone increasing firstly and followed by decreasing with the increase of the simulation depth under path 1,which shows that the stress unloading degree will significantly affect the Y direction progressive deformation characteristics of sandstone. In addition, the X direction principal strain of sandstone increases with the increase of the simulated depth under different stress paths, which shows that the deep effect is significant.