Coal permeability and crack distribution characteristics in unloading confining pressure experiments under different water pressures

This paper addresses the mechanical behavior and permeability characteristics of the unloading coal under different water pressures in the TOP2518-comprehensive- rock-testing system. With the use of the computed tomography scan tests, the 3-D crack distribution characteristics of the fractured coal are obtained and reconstructed. The difference in the 3-D crack distribution of unloading coal induced by different water pressures is also analyzed in detail. The results show that, as the water pressure changes from 0 MPa to 8 MPa, the peak stress of unloading coal gradually decreases, and that the variation degree of permeability of the coal samples increases significantly comparing with the initial permeability.