Experimental study of stress–permeability behavior of single persistent fractured coal samples in the fractured zone

Abstract

The coal and rock masses located in a fractured zone are generally subject to shear and tensile stresses and respective damages, which increase their permeability and produce new channels of gas migration. This directly affects the gas extraction and the safe mining of the adjacent coal seams. This experimental study of the single persistent fractured coal samples (SPFCS) in the fractured zone of the Huainan coal mine, China, investigates the stress–permeability relationships of the SPFCS under cyclic loading and unloading. The permeability of the SPFCS was found to be much higher than that of elastic coal samples and exhibited a decreasing trend with the effective stress. The longer the compression time, the greater the permeability loss, but the impact of the compaction time on the permeability loss gradually decreases with the increase in the compaction time. The mechanism of permeability loss and changes during the cyclic loading–unloading are analyzed based on the experiment results. The results show that the fracture surface crushing, re-arrangement, and compressional deformation of pulverized coal in the loading process lead to a drastic drop in permeability. Besides this, the axial permeability sensitivity to the confining stress is found to be much higher than that to the axial stress.