Abstract:
Violent gas outbursts are one of the most severe hazards in underground mining. When outbursts occur, a large amount of coal and gas is suddenly and violently ejected into the roadway and working area with the possibility of serious hazard and injury. Recent studies have shown that the physical behavior responsible for the energetic failure of coal is entirely consistent with coal viewed as a dual porosity-dual permeability-dual stiffness continuum where strength is proportional to effective stresses, and where effective stresses are controlled by both the pore pressure and varying stress field. Gas desorption driven by overstress is highlighted in this study as the key factor responsible for the increase in pore pressure close to the working face, and implicated together with elevated stress level, permeability evolution and drainage conditions in the triggering of outbursts. In this work, we incorporate the likely mass rates of desorption driven by an increase in abutment stress and mediated by permeability evolution to define the rates and distributions of gas pressure changes. The changing pattern of pressure redistribution is identified, and parametric studies are then performed to investigate all the key factors that influence the redistribution of pore pressure with respect to the deformation of the coal seam. Permeability evolution in the overstressed zone is determined by the evolution of porosity, which is attributed to both the change in effective stresses in the abutment and sorption-induced strain. This model is capable of predicting the potential risk ahead of the working face during mining and can be adapted to different conditions in terms of varying mechanical factors, coal properties and mining methods.
Introduction
Gas outbursts in coal mining are defined as the instantaneous and violent ejection of brittle coal, rock and a massive volume of gas, potentially damaging mining machinery, underground support and causing physical injury to personnel. It has been recognized as one of the most severe hazards in underground mining since its early reporting in the 1850s. More than 30,000 outbursts have occurred historically, of which reportedly the most disastrous accident caused 187 deaths in the Piast area of Poland in the Nowa Ruda Colliery, in 1941 (Lama and Bodziony, 1998). Nineteen outbursts driven by both of methane and carbon dioxide have been recorded in the Collinsville area, Australia since the first case killing seven men in 1954 (Harvey, 2002). Although the frequency of occurrence of outbursts has reduced in recent years with the development of technology and improved mining methods, outbursts remain a dangerous phenomenon in the global underground mining industry.
