To study damage deformation behaviour of low permeability soft coal rock subjected to the triaxial compression and pulsed pore water pressures

a series of experiments is conducted under different axial compressions and confining pressures using the RLW-2000 coal/rock rheometer. The results show that the general trend of stress-strain curve exhibits characteristically from sparse to dense and then back to sparse. In addition

both the cumulative and residual strains decrease with increasing confining pressure

however it is opposite with the increase of axial pressure. Meanwhile

the average dissipated energy of a cycle declines with the increase of confining pressure when the axial pressure is constant

but it increases with the increase of axial pressure when the confining pressure is constant. Moreover

the relationship between the average dissipated energy of a cycle and the confining pressure or axial pressure fits the exponential function. Finally

the overall trend of damage in the process of coal failure is calculated on the basis of the relationship between accumulated energy dissipation and damage

and the inverse function of Logistic equation is applied to fit the damage trend. Then the damage evolution model is obtained

which provides the basis for predicting the damage cycle of coal. The present results provide a theoretical evidence for the pulsed hydraulic fracturing on the low permeability soft coal seams under different ground stresses.