Failure Characteristics Of Overlying Strata In Shallow Coal Seam Mining And Setting Of The Water(sand)-proof Pillar

Based on the experience improving the upper limit of mining of Yanzhou mining area, I conclude the damage rule of shallow coal seam roof, use the fuzzy mathematics method on the relevance of the factors of bedrock pillar thickness,weathering zone thickness, mining thickness and thickness of Quaternary system and the height of the overlying rock caving crack to make clustering and fuzzy regression analysis, use the method of numerical simulation to analyze the failure characteristics of overlying strata under the condition of thin bedrock and thick coal seam.At last,taking the two and the No. four mining area of Xing Xing Zhuang as an example, this paper introduces the method of raising the upper limit of mining in the two and four mining area.The main conclusions are as follows:(1) With the increase of the number of layers, the height and thickness ratio between the height of the collapse zone and the water flowing fractured zone and the mining height decrease significantly. Increasing the thickness of the initial mining will lead to the increase of the height of the caving zone and the water flowing fracture zone, while increasing the thickness of the repeated mining will not lead to a significant increase of the water flowing fracture zone, greater the mining thickness is,the reduced amplitude of the decreased of the height of fracture zone decreases with the thickness of rock column will be greater.(2) By collecting the measured data of roof caving zone and fracture zone in the surrounding mining area, I cluster the data using the fuzzy clustering method and build the model of the fuzzy linear regression. Then, the fuzzy linear regression formula is obtained. The formula as follows:y=0.1532x1+0.4688x2 + A3 (0.0770,0.0268)x3 +1.7462x4(3) Using UDEC numerical simulation, it is found that the collapse of the caving zone in the coal seam mining after a long distance, then gradually compacted,gradually bear the upper load. When the bedrock column is thin, the loose layer is disturbed in the process of coal seam mining. The loose layer becomes an important part of land subsidence. And in the process of relieving the upper pressure and reducing the ground subsidence, the weathering zone is more obvious than that of the thick bedrock column.(4) The water abundance of the lower Quaternary aquifer is totally weak, partial area is medium or weaker. And the water head of the aquifer has been reduced to 20.41?57.7m,which is in the condition of no pressure to micro pressure,and the recharge condition is weak. Because the safety degree of the improvement of the upper limit of the mining is higher, so, even if the partial section of the water flowing fractured zone spread to the Quaternary bottom, but because of the weak aquifer water bearing and low water level conditions, infiltration water generally won't be big,which won't leads to serious water inrush accidents.