Effect of moisture content on methane adsorption- and desorption-induced deformation of tectonically deformed coal

Intermolecular forces that act between moisture and the atoms of the coal structure have a significant influence on methane adsorption- and desorption-induced deformation in coal. After analyzing the porous characteristics and existing forms of moisture in coal, both the adsorption-induced swelling and the desorption-induced shrinkage deformation experiments were carried out under the conditions of varying moisture content, constant temperature, and variable equilibrium pressure. Both the swelling and shrinkage volumetric strains with different coal moisture contents were fitted by Langmuir-type equations in which the fitting coefficients were functions of the moisture content. It was found that there is a lag between the swelling curve and the corresponding shrinkage curve, and a variable known as the hysteresis rate was defined to illustrate this characteristic. A mathematical model of swelling and shrinkage deformation that considers the effect of moisture content was established based on the experimental results and analysis.