Research and microscopic analysis of seepage characteristics of sandstone under low-frequency cyclic loading

Abstract

The change of rock permeability properties under cyclic load is of great significance to the safety of underground engineering. However, there are few studies on triaxial seepage tests under different cyclic loads, and most of them have not carried out microscopic mechanism analysis. Therefore, in this paper, the seepage test of intact sandstone under different cyclic loads was carried out under low confining pressure. The test used sine waves to simulate low-frequency seismic waves, highlighting the permeability of underground water-bearing engineering rock mass with vibration frequency and amplitude under low-frequency source disturbance Variations and test results show that in the sandstone triaxial stress-strain curve, from the compacted section, the elastic section to the expansion section, the permeability of the rock gradually increases, and the sensitivity to cyclic load also increases. At the same time, the damage threshold of the rock gradually decreases, and the rock will break even in the elastic section. Under low confining pressure, the loading amplitude has a greater impact on rock permeability than the loading frequency under low-frequency cyclic loading. The loading frequency and loading amplitude can be comprehensively characterized by the average loading rate. Then, using nuclear magnetic imaging technology to change the microstructure of the rock sample before and after the test, the analysis shows that the effect of different cyclic load parameters on the permeability of the rock sample is actually obtained through the effect of force on pores and cracks. For dense rocks, The increase in permeability caused by cracks is even greater.