Mining‐disturbed coal damage and permeability evolution: Model and validation

Coalbed methane (CBM) is not only the material cause of gas explosion and coal‐gas outburst disasters during underground coal mining, but also a kind of clean energy. Coal permeability is an important parameter for CBM drainage. Although many coal permeability models have been developed in the past decades to describe the permeability evolution characteristics under elastic state, few of them could explain the permeability behavior of the mining‐disturbed coal which is often the situation of CBM drainage during underground coal mining. The paper analyzed the mechanical factors affecting the damage‐permeability characteristics of mining‐disturbed coal, proposed the concept of the deviatoric stress ratio (DSR), and then established the statistical damage and permeability evolution models based on DSR. Results show that the deformation and damage of coal is controlled by the deviatoric stress and minimum principal stress. The plastic damage degree of coal mass becomes more serious with DSR increase, which leads to the improvement in permeability. The damage constitutive model was established based on the Weibull distribution function and DSR, and then the permeability model of mining‐disturbed coal was built combining the Kozeny–Carman equation. The acoustic emission (AE) and permeability experiments of the loading and unloading coal sample were conducted. After normalizing and fitting the accumulative AE counts, the damage and permeability evolutions with respect to DSR were found out. The model‐predicted permeability could match with the experiment results, verifying the reliability of the theoretical permeability model. The purpose of this paper is to provide a new approach for modeling damage and permeability of mining‐disturbed coal based on DSR. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.