Research on sandstone dilation behavior and non-coaxiality under different stress Lode angle conditions

In actual underground engineering excavation,the rock is in a mining stress state,and its mining stress path is represented by the stress Lode angle. Based on the multifunctional true triaxial fluid-solid coupling test system,various true triaxial mechanical tests with same hydrostatic pressure and different stress Lode angles were carried out to study the effects of different stress Lode angles on the dilation characteristics and non-coaxiality of sandstone. The test results show that the increase of stress Lode angle reflects to some extent the effect of unloading action on the deformation of sandstone true triaxial test. Comparing the amount of principal stress variation for stress Lode angle from -30 to 0° and 0 to 30°,it can be found that the maximum principal stress variation is more uniform,the middle principal stress variation decreases and the minimum principal stress variation increases. As the stress Lode angle increases,the degree of compression of the maximum principal strain decreases,the intermediate principal strain changes from expansion to compression,and the degree of expansion of the minimum principal strain increases,and the stress Lode angle changes from -30° to 30°,and the volume strain shows a tendency to decrease and then increase as the maximum principal strain increases. Introducing the strain-partial stress flexibility, with the increase of the stress Lode angle,the effect of generalized shear stress on the compressive deformation in the direction of the maximum principal stress is weakened,and the effect on the expansion deformation in the direction of the minimum principal stress is first enhanced and then tends to be smooth. The volume strain partial stress flexibility shows an overall decreasing trend. The non-coaxiality is manifested by the non-coincidence of stress and strain paths,and the strain paths under different stress Lode angles all evolve toward the low Lode angle. With the introduction of deflection, the stress Lode angle changes from -30° to 30°,and the deflection shows a rising and then decreasing trend.