Experimental study of the evolution of permeability in coal containing gas during short-term creep under multi-stage loading

摘要

Aiming at understanding the evolution characteristics of permeability in coal masses containing gas during creep, samples of coal containing gas were collected from the No. 3 coal seam of Rundong coal mine, Yangcheng, China for analysis. The seepage is tested during the creep process in multi-stage axial load apparatus under different confining pressures using a self-developed multi-stage triaxial stress loading device allowing analysis of seepage during creep processes. Experimental results shows that: (I) obvious attenuation creep deformation and static deformation appeared during the creep process caused by multi-stage loading under low stresses, and the permeability decreased during the loading process and creep stage. The permeability decreased at a high rate in the initial stages of testing, gradually reaching a stable value and, it changed in the opposite sense to the axial deformation. Moreover, high confining pressures had certain inhibiting effects on the change in permeability of the coal samples; (2) The permeability varied slightly in the attenuated, and steady, stages under the failure stress of creep, and it decreased in the attenuated stage, while it linearly increased under steady state conditions. In the accelerated stage, the permeability increases significantly and it is several times greater than the initial permeability in the steady creep stage when the coal body is damaged; (3) In the creep damage stage, the changes in the permeability and volumetric strain conformed to an exponential function.