Abstract
In order to determine the reasonable height of water-proof coal (rock) pillar when mining multiple coal seams under aquifer, this paper analyzes the expansion height of water-conducting fracture zone when coal seams mining. Considering the expansion law of water-conducting fracture zone in coal seams mining, two schemes of coal seams mining in upper and lower groups and one-time mining of all coal seams are designed for comparative analysis, and the height of water-proof coal (rock) pillar is determined based on the expansion height of water-conducting fracture zone. The results show that the height of water-proof coal (rock) pillar is calculated as 91.08 m when mining upper and lower groups and 105.46 m when mining all coal seams at the same time. According to UDEC numerical simulation results, the height of water-proof coal (rock) pillar is 56.08 m when mining upper and lower groups and 86.36 m when mining all coal seams at the same time. Comparing the results of theoretical calculation and numerical analysis, the maximum value is selected as the final result, and the reasonable water-proof coal (rock) pillar height is determined to be 105.46 m.
Highlights
After underground coal seam mining, the migration and destruction of overlying strata will form a hydraulic connection channel between stope and surrounding waterbearing rock stratum, which threatens the safety of mine production
E above stratum structure features have both advantaged and disadvantaged factors for mining coal seam group under water-bearing rock stratum. e advantaged factor is that there is no hydraulic connection between the effective water-bearing rock strata of bedrock, the relative waterproof strata, and the weak water-bearing rock stratum in the area, because there are thick multilayer argillaceous waterproof strata. e disadvantaged factor is that the roof and floor of minable seam are extremely unstable and soften strongly when meeting water, so it is necessary to analyze the height of water-conducting fracture zone and determine the water-proof coal pillar
When there are extremely hard strata in the overlying strata of coal seam roof, the suspended roof can be formed after mining, and the formula of caving zone is where Hm is the maximum caving zone height; M is the thickness of coal seam mining; K is the crushing expansion coefficient of caving rock, and α is the dip angle of coal seam
Summary
After underground coal seam mining, the migration and destruction of overlying strata will form a hydraulic connection channel between stope and surrounding waterbearing rock stratum, which threatens the safety of mine production. Reasonable height of water-proof coal (rock) pillar can effectively inhibit the development of water-conducting fracture zone of overlying strata in mining field and ensure that the working face is not threatened by water disasters during mining. At present, when determining the water-conducting fracture zones with different overlying strata lithology in gently inclined and inclined thick coal seams in China, the calculation is mainly based on the formula in Regulations for Coal Pillar Retention and Coal Mining in buildings, water bodies, railways, and main roadways [33]. In the calculation process of the lower coal group, firstly calculate the height of the caving zone, determine whether the caving zone affects the overlying coal seam, and calculate the expansion height of water-conducting fracture zone according to the relevant formula. According to formula (4), it is determined that the height of water-proof coal (rock) pillar of grouping mining is 91.36 m, and the height of water-proof coal pillar of simultaneous mining of all coal seams is 105.46 m
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