Determining Gas Pressure in Rock Mass Stratification Cavities with the Hazard of Out-of-Soil Methane Outbreaks

Methane outbreaks from mine excavation soils occurring in coalmines cause serious damage to enterprises and threaten the life and health of miners. The normative forecasting method of the phenomenon was studied at the end of the 20th century. It assumes high error rates of the second kind and therefore requires improvement. The mechanism of hazardous area formation assumes the occurrence of stratification cavities in the rocks of mine excavation soils filled with methane under high pressure, followed by the loss of containment of the cavity and a gas explosion. The acceptance of gas pressure in the cavity at the level of methane geostatic pressure for the calculation is considered one of the possible causes of the insufficient accuracy of the method mentioned above. The study is dedicated to the determination of the balanced pressure of methane in the stratification cavity in conditions of a leak-tight system «methane source — stratification cavity». Due to accepting the assumption of continuity of cavity volume and leak-tightness of the system «methane source — stratification cavity», determining the balanced pressure of methane in this system has been reduced to a static problem. In the course of problem-solving, a quadratic equation based on the Boyle — Mariotte law and a formula for the phase balance of methane in coal has been developed. The values of the balanced pressure of methane in the stratification cavity have been calculated for various mining and geological indices. Actual indices of the rock mass have been adopted as the initial data. The obtained values of balanced pressure are approximately three times lower than the formation pressures existing in natural conditions. Therefore, the assumptions regarding the invidious comparison of methane pressure in the stratification cavity with the geostatic pressure when determining the probability of soil rock destruction and the following methane outbreak have been fully confirmed.