Study On Evolution Of Mining-induced Fractures Field And Its Coupling Effect With Gas Seepage Under The Conditions Of High-strength Underground Mining

The coal-gas bursts are serious in china. Most of accents are accrued at high and extra-high seams under conditions of high-strength mining method, such as fully mechanized mining with top coal caving and with large mining height.However, the mechanism, forewarning and preventaion of coal-gas burst and gas disaster are inadequate research. Especially, the research is insufficient to the evolution of mining-induced fracture and its effect on gas seepage.By taking coal mass of high-strength underground mining as the research object, the combination method of laboratory experiment and experiment on site theoretical analysis and numerical analysis are used, multi-disciplinary research of crossing which combines mining engineer. The main aspects can be seen as the following:(1) The method of borehole camera, single scan line method and sampling window method were used to study the mining-induced fractures field. Based on the analysis of mine-induced stress distribution, the concept of "mining-induced fractures field" and its zoning were proposed.(2) For to simulate coal mass fractures and their's evolution, proper method was adopted to characterize the heterogeneity. The concrete method is that pseudo-random number generation by using the Monte Carlo method to random assign material parameters. After modified Mohr-Coulomb model of FLAC^3D, the Fracture. dll of elasto-brittle-plasticity was complied by using the software VS2005. Takes field observation data as initial state, the mining-induced fractures extension and cross was simulated. And the gas flow was researched in this process.(3) For to find out the effect of high-strength underground mining to gas seepage, Series of research on coal samples permeability sensibility were experimentized, which mainly included that uniaxial (triaxial) compression test, scale effects test of permeability sensibility, pore pressure test of permeability sensibility and parallel test of permeability sensibility.â‘ It is shown that the permeability of coal samples with pressure can be fitted by negative exponential law. Axial compression had more influence for the permeability than confining pressure.â‘¡With the scale of coal samples increase , the absolute value of the slope of the K—p predicted curves under load-on statutes turns to smaller. With K₀ increases, the absolute value of the slope of K—p predicted curves under load-on statutes turn larger.â‘¢To low-permeability coal mass, the gas seepage is affected by the slippage effect with the low pore pressure and seepage velocity.â‘£With the force condition change of coal mass, the transmission capacity will change. And the main seepage direction and flow contribution will also change.(4) After these researches, the permeability variation was analyzed with evolution of mining-induced fractures field. The coupling equation of seepage-stress is achieved. By numerical simulation research of different scheme, the gas flow progress was analyzed.(5) The numerical simulation of gas drainage at 3207 workface in Wangpo. Mine was achieved by using the COMSOL Multiphysics software. Fracture orientation and strike made the main function during gas seepage.