The Impact of a Crack of Directed Hydraulic Fracturing on the State of the Rocks of a Formation Working Roof

Results of the solution of the carboniferous massif stress state problem in the vicinity of the preparatory (seam) mine working in the presence of a hydraulic fracturing located in solid rocks above the working and reaching its final design dimensions are provided. The impact of liquid pressure and the distance from the crack to the working roof on the values of parameters of the extremely stressed marginal seam zone has been studied. The problem is solved within the framework of the modernized model of the geomechanical state of a carboniferous massif containing a coal seam, the working passing through it, and the geological disruption in the form of a narrow gap where the liquid pressure acts instead of a filler. The model is based on methods of rock limiting state theory and elasticity theory. The stress distribution in the limiting marginal zone of a seam that occurs in accordance with the general and the special Coulomb — Mohr criteria is determined by the characteristics method. Using the statics axiom of the replacement of bonds with reactive forces makes it possible to reduce the problem to a boundary value problem of the elasticity theory and address it by the method of boundary elements where its version in the form of dummy load method is used for the working contour, whereas for the hydraulic gap contour, a discontinuous displacement method is applied. The results of the hydraulic fracturing method for a number of initial parameters have been analyzed. According to the analysis, a hydraulic crack increases the stress zone parameters and causes tensile stresses in the working roof, which, along with the increase of liquid pressure in the crack, cause vertical fractures.