Abstract:

Much attention should be paid to the permeability of broken rocks in goaf for the sake of the gas outburst and disaster prevention. Using a special device together with the MTS815.02 Rock Mechanics Test System, we tested the permeability of broken coal during its compacting process, getting the relations between the axial stress and the differential seepage pressure and between the pressure gradient and the seepage velocity. The effects of axial stress, grain size, and seepage velocities on the permeability coefficient are analyzed. The results show that the permeability of broken coal with different sizes is closely related with its compaction state: (1) the maximum value of seepage pressure will increase 3.28-166.47 times as the axial stress changing from 5 MPa to 15 MPa; the permeability coefficient of broken coal will decrease one magnitude; and (2) for a constant seepage velocity, the differential seepage pressure and the axial stress can be expressed by an exponential function; and (3) for a constant axial stress, the pressure gradient and the seepage velocity can be also expressed by an exponential function; and (4) the permeability coefficient of broken coal will decrease with the increase of axial stress, having a logarithm functional relation between them.

Key words: broken coal, axial stress, seepage properties, test