Mechanical failure mechanisms and forms of normal and deformed coal combination containing gas: Model development and analysis

In coal mining, coal seams often contain several normal coal layers and deformed coal layers in the same region. However, the existence of deformed coal may promote the occurrence of coal and gas outbursts. To analyze the role of failure of different combinations of deformed coal on coal and gas outbursts, force analysis of normal and deformed coal combinations containing gas was carried out, and the expressions of interfacial stress induced by uncoordinated horizontal deformation were first derived in this paper. The results showed that the additional interfacial stresses are affected by the external stresses, internal gas pressure, gas sorption-induced swelling deformation and mechanical parameters of coal and that the additional interfacial stresses on the normal coal and deformed coal are equal and opposite. Then, based on the Mohr-Coulomb criterion and uncoordinated deformation, the mechanical failure mechanisms and forms of combinations containing gas under ideal conditions were analyzed. We found that there are seven failure forms for the combination containing gas, and in most cases, the destruction of the combination is caused by the structural failure of deformed coal. Finally, the failure mechanisms of the combination due to mining were discussed using the parameters from the Qinshui Basin. The results showed that failure is more probable at the interface between the deformed coal and normal coal bodies and that the existence of deformed coal can promote the damage of normal coal. These research results can help us to better understand the role of mechanical failure in coal and gas outbursts within combinations, and provide a theoretical basis for the control of coal and gas outbursts.