Pressure relief, gas drainage and deformation effects on an overlying coal seam induced by drilling an extra-thin protective coal seam

Numerical simulations and field tests were used to investigate the changes in ground stress and deformation of, and gas flow from, a protected coal seam under which an extra-thin coal seam was drilled. The geological conditions were: 0.5 meter min-ing height, 18.5 meter coal seam spacing and a hard limestone/fine sandstone inter-stratum. For these conditions we conclude: 1) the overlying coal-rock mass bends and sinks without the appearance of a caving zone, and 2) the protected coal seam is in the bending zone and undergoes expansion deformation in the stress-relaxed area. The deformation was 12 mm and the relative defor-mation was 0.15%. As mining proceeds, deformation in the protected layer begins as compression, then becomes a rapid expansion and, finally, reaches a stable value. A large number of bed separation crannies are created in the stress-relaxed area and the perme-ability coefficient of the coal seam was increased 403 fold. Grid penetration boreholes were evenly drilled toward the protected coal seam to affect pressure relief and gas drainage. This made the gas pressure decrease from 0.75 to 0.15 Mpa, the gas content de-crease from 13 to 4.66 m3/t and the gas drainage reach 64%.     

高瓦斯煤层群保护层开采卸压效果数值模拟

为合理选择保护层,针对高瓦斯突出煤层群安全开采问题,分析了保护层开采的保护作用机理,即保护层开采可对被保护层起到卸压增透作用,改善被保护层的瓦斯抽放效果是解决煤与瓦斯突出问题及瓦斯灾害的重要技术手段;卸压对煤与瓦斯突出及瓦斯问题的解决具有决定作用.针对某矿高瓦斯突出煤层群生产地质条件,采用FLAC3D数值软件模拟2个非突出煤层作为保护层开采时的卸压效果,并对其进行了分析比较,研究结果可为保护层的合理选择提供参考依据.     

巨厚火成岩对下伏煤层煤与瓦斯突出事故控制作用

以海孜煤矿120m巨厚火成岩下伏煤层群12个煤样为研究对象,采用工业分析、压汞试验和显微组分定量的方法,对比分析了7,8,9,10煤层的多元物性参数和与火成岩距离的关系.结果表明:煤层靠近巨厚火成岩,连续煤样的挥发分Vdaf有减小的趋势,灰分Ad有增加的趋势.煤样的孔隙率和比表面积有缓慢增大后急剧下降的趋势,这和岩浆侵入7煤有关.镜质组反射率Rm取值范围为2.358%～2.777%,煤层靠近岩床,Rm值有递增的趋势,煤的变质程度和成熟度提高.巨厚火成岩的热演化范围大于168m(1.4倍岩床厚度).火成岩像个密封盖,对下伏煤层瓦斯有圈闭作用,容易发生煤与瓦斯突出事故.     

Principle and engineering application of pressure relief gas drainage in low permeability outburst coal seam

With the increase in mining depth, the danger of coal and gas outbursts increases. In order to drain coal gas effectively and to eliminate the risk of coal and gas outbursts, we used a specific number of penetration boreholes for draining of pressure relief gas. Based on the principle of overlying strata movement, deformation and pressure relief, a good effect of gas drainage was obtained. The practice in the Panyi coal mine has shown that, after mining the Cllcoal seam as the protective layer, the relative expansion deformation value of the protected layer C13 reached 2.63%, The permeability coefficient increased 2880 times, the gas drainage rate of the C13 coal seam increased to more than 60%, the amount of gas was reduced from 13.0 to 5.2 m3/t and the gas pressure declined from 4.4 to 0.4 MPa, which caused the danger the outbursts in the coal seams to be eliminated. The result was that we achieved a safe and highly efficient mining operation of the C 13 coal seam.     

Fissure evolution and evaluation of pressure-relief gas drainage in the exploitation of super-remote protected seams

Based on nonlinearity contact theory and the geological structure of the Xieqiao Coal Mine in the newly developed Huainan coal field, rock movements, mining fissures and deformation of overlying strata were simulated by using the interface unit of FLAC3D to evaluate the pressure-relief gas drainage in the exploitation of super-remote protected seams. The simulation indicates that the height of the water flowing fractured zone is 54 m in the overlying strata above the protective layer. The maximum relative swelling deformation of the C 13 coal seam is 0.232%,while the mining height is 3.0 m and the distance from the B8 roof to the C13 floor is 129 m, which provides good agreement with a similar experiment and in situ results. The feasibility of exploitation of a super-remote protective coal seam and the performance of the pressure-relief gas drainage in a super-remote protected layer are evaluated by comparisons with practice projects. It demonstrates that the relieved gas in the super-remote protected layers could be better drained and it is feasible to exploit the B8 coal seam before the C13 super-remote protected coal seam. The method is applicable for the study of rock movements, mining fissures and deformation of the overburden, using the interface unit to analyze the contact problems in coal mines.     

Overburden fracture evolution laws and water-controlling technologies in mining very thick coal seam under water-rich roof

Considering the danger of water inrush in mining very thick coal seam under water-rich roof in Majialiang Coal Mine, the universal discrete element (UDEC) software was used to simulate the overburden fracture evolution laws when mining 4# coal seam. Besides, this study researched on the influence of face advancing length, speed and mining height on the height of the water flowing fractured zones (HWFFZ), and analyzed the correlation of face advancing length and change rules of aquifer water levels and goaf water inflow. Based on those mentioned above, this research proposed the following water-controlling technologies: draining the roof water before mining, draining goaf water, reasonable advancing speed and mining thickness. These water-controlling technologies were successfully used in the field, thus ensured safely mining the very thick coal seam under water-rich roof.