Evolution of Broken Coal Permeability Under the Condition of Stress, Temperature, Moisture Content, and Pore Pressure

Abstract

The permeability of broken coal is not only mainly controlled by coal structure, but also unavoidably influenced by variations of stress, particle size, moisture content, and temperature. In this paper, a self-designed experimental device was utilized to investigate the permeability evolution of seven coal samples with different particle size ratios during the loading processes under the condition of temperature, water content, and pore pressure. The results show that both the permeability and the porosity are negative exponential functions of axial stress. Under the same stress, the porosity and the permeability decrease with the increase of the particle size and the particle size range of the coal samples; in the process of compaction, the larger the particle size and the particle size range of the coal samples, the higher the change rate of the porosity and the permeability. Under the same stress, any increase of temperature, water content, or pore pressure would cause the decrease of the permeability of the coal samples, i.e., they are negatively correlated. With the establishment of the permeability calculation model of the coal samples under different temperatures, water contents, and pore pressures during the loading processes, the permeability of different locations in different environments can be speculated. Based on the estimated data, the air leakage in different areas can be obtained to determine the spontaneous combustion zone in goaf, which is crucial for fire prevention and control in goaf.