Coal permeability evolution during damage process under different mining layouts

Abstract

ABSTRACT Coal permeability is akey component that affects gas migration. Considering seepage behavior of gas during mining is critical for improving the production profile of coal-bed methane (CBM) wells, and preventing coal and gas outburst. Aseries of seepage tests have been carried out to simulate the coal permeability evolution law during mining-induced actions. Coal damage has been assessed by using atri-axial servo seepage testing system. The results show that the coal permeability under PCM, Top-coal Caving Mining (TCM) and NM are all kept constant before the deviatoric stress reaches the peak strength, then increases mildly and finally increases rapidly. The effective stress decreases during confining pressure relief, and the permeability increases exponentially with the decrease of effective stress, which is quite different from the traditional triaxial compression test. According to continuum damage mechanics, adamage constitutive model of coal was proposed to characterize coal mechanical characteristics by mining-induced activities. Furthermore, according to the matchstick model, anew coal permeability model is proposed, which could accurately reflect seepage behavior under different mining layouts.