Study on the relation between damage and permeability of sandstone at depth under cyclic loading

The damage and permeability evolution of rock under stress is of great significance to engineering safety. In this paper, the evolution law of rock damage and permeability is studied by means of acoustic emission (AE) seepage experiment on deep roof sandstone with cyclic loading. Characterization of damage uses the changes in acoustic emission fractal characteristics and compression parameter which based on elastic modulus. The experimental results show that the AE events has fractal characteristic, in which the AE b-value and correlation dimension can represent the damage of rock. When the fractal characteristic value of AE increases, it indicates that the rock is in the compaction stage and the damage is not obvious. When the fractal characteristic value of AE drops, it indicates that the rock was damaged, and the permeability increase. Under the cyclic load increasing step by step, the elastic modulus first increases and then decrease. Introducing compression parameter C to characterize the state of compaction and damage, it is obtained that the rock damage state and hydrostatic permeability show a power law function relationship with porosity and have the same monotonicity. When compression parameter is less than zero, the evolution law of permeability and damage can be described by functional relationship between hydrostatic permeability K and compression parameter C.