Experimental Study on Gas Seepage Characteristics of Axially Unloaded Coal under Different Confining Pressures and Gas Pressures

Abstract

Protective coal seam mining can not only effectively prevent coal and gas outbursts in mines, but also provide stress unloading space for the protected coal seam. The coal body in the protected coal seam might undergo deformation, internal damage and structural damage, which changes its gas seepage characteristics. This study aims to explore the variations of permeability of the coal body in the protected coal seam under axial unloading. With the coal body from the outburst coal seam in the Huaibei mining area as the research object, experiments were conducted to explore the gas seepage characteristics of axially unloaded coal body under different confining pressures and gas pressures, using the TAWD-2000 coal-rock mechanics-seepage experimental system. According to the results, with respect to the gas seepage, the variations of permeabilities of axially unloaded coal samples are closely related to their deformation and damage. As the confining pressure and gas pressure rise, the difference between the permeability at the final failure point and the initial permeability rises at a decreasing rate. The experiments fully demonstrate that the protective coal seam is technically important for the unloaded gas drainage and the coal and gas outburst prevention of the protected coal seam. Under different confining pressures and gas pressures, the permeability of axially unloaded coal varies to different extents and at different rates. The mining scheme for the protective coal seam should be designed in accordance with its confining pressure and gas pressure. This study is of guiding significance for the prevention and control of coal and gas outbursts in coal seam groups.