Study on the evolution law of rock microstructure under loading and unloading water pressure

The internal microstructure of rock under different pressures determines the stability of underground engineering. In this paper, the internal microstructure of rock under different loading and unloading water pressure is monitored by NMR in real time. The results show in the stage of loading and unloading water pressure, the variation law of water pressure is basically the same as that of porosity and permeability. During the process of increasing water pressure, the pore expansion in the rock is active and the porosity and permeability increase obviously. While the change of porosity and permeability is small during the unloading pressure. When the rock is unloaded to the same stress level, the porosity is obviously greater than that when the rock is loaded to the same stress level, which is caused by the plastic deformation of the rock. The permeability is significantly lower than when loaded to the same level, which is mainly related to the reduction of macropores during unloading, which fully indicates that the permeability is not only related to the size of porosity, but also to the degree of penetration between the pores.