| Because gob is unevenly filled by the fallen direct roof stratum in long wall top coal caving of steeply inclined thick coal seam, the deformation, fracture pattern, energy distribution and stress transfer of the main roof stratum present asymmetric feature. Therefore, it is of great importance to study main roof fracture mechanism in details and strong mine pressure control method of steeply inclined coal seam, which is significant to enrich the theory of mine pressure and direct mining practice.Based on the geologic condition of steeply coal seam in Wang jia-shan Colliery, by means of laboratory tests, theoretical analysis, numerical simulation and monitoring, the initial and periodic fracture mode of main roof stratum are revealed. The asymmetrical characteristic of stress distribution and evolution law are presented. The dangerous region identifying method and directional elastic energy releasing method for control strong mine pressure is put forward.The main results of this dissertation are listed as follows:(1) Based on the theory of elasticity, an analytic model of thin plate is established under consideration of vertical and lateral loads for the main roof above steeper inclined coal seam. The stresses distribution in the up and low surface is analyzed, the initial fracture trajectory development and failure zone evolution are revealed. The initial fracture mode of the main roof, termed as "V-Y" is put forward. The study shows that the spatial sequence of initial fracture follows "upper-middle to lower-middle, and upper to lower" of the mining face. In cooperating with numerical modeling and monitoring, the asymmetrical and sequential characteristic of stress distribution in the main roof stratum and the mining induced pressure in working face are verified during initial fracture;(2) Based on the theory of elasticity, thin plate mechanical analytic models of the main roof stratum transformed from small triangular, big triangular and trapezoid above the caving gob are established during the mining face advancing in steeply inclined thick coal seam. The stress distribution in the up and low surface of the main roof stratum in three types as mentioned above are calculated, the laws of fracture trajectory development and failure zone evolution are revealed. The periodic fracture mode of main roof stratum, termed as "Quadrangle" is put forward with respect to mining of the steeply inclined thick coal seam. The study shows that the spatial sequence of periodic fracture is "lower-middle to upper-middle, and upper to lower" of the mining face. In cooperating with numerical modeling and monitoring, the asymmetrical and sequential characteristic of stress distribution in the main roof stratum and the mining induced pressure in working face are verified during periodic fracture;(3) The stress distribution and evolution law of steeply inclined thick coal seam (group) are revealed. The asymmetrical distribution characteristics of abutment pressures in mining pressure area is arc-shaped, while rectangle-shaped in stability area are found. The periodic fracture mode of main roof stratum in block working face is also follow "Quadrangle" fracture mode is proved;(4) By means of synthetic index method, statically indeterminated beam theory and statistical theory, the hierarchical dangerous region identification and critical location monitoring method of strong mine pressure are put forward with respect to different scales of minefield-working face-near area-point, and the corresponding control schemes of strong mine pressure are designed for the different dangerous levels;(5) The disaster-causing mechanism of strong mine pressure in extra thick steeply inclined seam is studied, and conclusions were made as follows:The hybrid strong mine pressure could happen at the upper part of working face, because of the combined effect of abutment pressure and main roof fracture. The mine induced pressure could happen at the middle part of working face, and energy concentrated mine pressure prone to happen at the lower part of working face;(6) The herringbone energy bifurcation after elastic energy releaf ahead of mining face roof is found through the numerical simulations, which is the major disaster source after pressure relief on the roof. The directional elastic energy releasing method to control strong mine pressure is put forward accordingly. The monitoring data shows that this method is significance in reduction of the roof pressure, the weighting interval, as well as the probability of associated disasters. |
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