Experimental study on damage and the permeability evolution process of methane-containing coal under different temperature conditions

Abstract

Temperature change in coal will lead to the expansion and propagation of micro-cracks, and this progressive temperature-induced failure is defined as thermal damage. Understanding coal permeability as impacted by thermal damage is crucial to the detection of coal and gas hazards in deep coal mining. In this study, tri-axial compression experiments were performed to examine the damage and the permeability evolution process of methane-containing coal under different temperatures (30 °C, 50 °C and 70 °C). The results demonstrate that under a low external stress, the overall coal permeability decreases with the rise of temperature. More specifically, in the linear elastic stage, the coal elasticity modulus drops as the temperature becomes higher while the permeability remains nearly constant. In the yielding and post-failure stages, the tri-axial compressive strength of coal weakens with the rise of temperature, whereas the permeability increases slowly first and then jumps sharply. A coal damage constitutive model considering the temperature effect and a coal permeability model incorporating the thermal damage in the complete stress-strain process was developed. It is found that results from the coal damage model and the proposed coal permeability model agree well with the experimental results. The proposed coal permeability model can be used to characterize coal permeability variation from the plastic state to the post-failure state in areas adjacent to the underground coal excavation face under different temperature conditions.