Abstract: Coal damage by adsorbed gas has been observed and detected in a large number of experiments. Under the action of the adsorbed gas, the adsorption strain of coal is firstly generated, and then coal microstructure is rearranged, which will induce the coal damage and further deteriorate mechanical properties of coal. However, this adsorption-induced damage is usually ignored in the current coal-gas interaction models. Hence, it is necessary to propose a mechanical model for dual porosity medium, considering the adsorption-induced coal damage. In this study, a novel mechanical model was developed to accurately describe coal-gas interactions, including the routine mechanistic effect and the adsorption-induced internal swelling stress. Besides, the additional mechanical damage caused by these two coal mechanic actions was also studied. Research results show adsorption-induced coal damage, mostly in tensile mode, rearranges coal microstructure, and causes significant reductions of coal strength and Young’s module. It is found that the tension damage is the main reason for the gas adsorption-induced damage. In addition, gas with higher adsorption capacity will result in a larger rearrangement of coal microstructure and more significant damage, and it even may cause a new failure pattern. Furthermore, supercritical CO2 with a higher adsorption capacity results in greater damage and causes larger alterations of coal strength and Young’s module.

Key words: swelling stress, local strain, global strain, adsorption-induced damage, strength