Evolution of cracks at the edge of a gas-bearing coal seam in its stationary development

In this paper, we consider conditions under which the gas enclosed in the main crack located at the edge of a coal or rock formation can produce fracture of the formation. Kinetic theory is developed for two competing physical processes: formation unloading due to rock pressure and gas filtration from the crack cavity into the surrounding massif. The first process promotes fracture, and the second leads to a decrease in the gas pressure causing he fracture. The evolution of the crack is determined by the ratio of the rates of these processes. It is found that a modified Griffiths criterion is a necessary but not sufficient condition for fracture. For formation fracture, it is also necessary that the unloading rate to the filtration rate exceed a certain threshold value.