Sapegin V. Development of method for calculating of the dynamic stresses in the near borehole zone of coal-rock massif by actions of working agents

The object of study: the process of non-stationary deformation of coal-rock massif by actions of working agents in boreholes. The purpose of the study are to establish of change regularities of inertial dynamic tensile stresses in the near borehole zone of gas-bearing coal-rock massif by actions of working agents and to develop, on its basis, the method of tensile stresses calculation for determining of rational parameters of ways for degassing intensification, which will reduce the gas content of coal seams, improve the safety and efficiency of their mining. Subject of study: change regularities of the inertial dynamic stresses that occur in the massif at relieving of working agents in the boreholes. Methods: continuations of the initial conditions method, the method of running wave, asymptotic method of two-point Pade approximation, gas dynamics methods, method of Fourier integral transformation, method of Fourier variables separation, method of successive approximations and methods of the theory of elasticity, experimental and analytical methods of mine gas emission observations from an massif into the boreholes. It has been found that the rate of pressure velocity relief of working agent is directly proportional to the pressure in the initial moment of relief and elastic wave velocity in the working agent and inversely proportional to the length of the borehole. It has been developed the procedure and method for calculating of the maximum tensile stressed and the regularity of the maximum tensile stress from the forces of inertia: tensile stress is directly proportional to the value of the internal pressure and the radius of the borehole, and inversely proportional to the velocity of elastic wave in massif and time of pressure relief. The practical significance of the results: the procedure for determination of dynamic tensile stresses from impact of various working agents on gas-bearing tight massif was developed; the calculation dependences for technical applications that allow by simple way to perform analysis of the stress state management of gas-saturated medium without solving complex dynamic tasks were obtained; the procedure for determination of the natural filtration parameters for a stress gas-bearing massif that allows according to changes of the gas pressure in the boreholes in time to receive additional information about the gas emission process: gas mass flow from the massif, its filtration rate and time drainage was developed; by solving of the A.N. Krylov problem the method of tensile stresses calculation, which allows in a simple way to determine the rational parameters of ways for degassing intensification using various working agents was developed. It has been developed the standard SOU 10.1.05411357.006: 2007 "Degassing of coal seams and enclosing rocks using gas gathering working. Degassing Schemes", which by the order number 546 of 7.12.2007 of Ministry of Coal Industry of Ukraine introduced in the coal mines of Ukraine. It has been developed the procedure for determination of natural filtration parameters for gas-bearing coal-rock massif and transferred to the practical using in PJSC "Krasnodonugol". Expected annual economic effect from the introduction of methods for determining of natural filtration parameters of coal-rock medium was 48.6 thousand UAH per one preparatory tunnel. The investigation results recommend to use in coal mines, design and research institutes, which solve the problems of increasing process of underground coal mining safety, development and introduction of new and improvement of existing technologies for underground coal mining enterprises.