Research On The Damage Law Of Roof Overburden And Height Of Water-conducting Fracture Zone In Longfeng Coal Mine Of Qianbei Coalfiel

Coal seam mining causes damage to the overlying strata,which is easy to form a water channel and threaten the safe production of coal mines.Based on the National Natural Science Foundation of China,this paper takes Longfeng Coal Mine in the Northern Guizhou Coalfield as the engineering background,comprehensively uses field investigation,theoretical analysis,numerical simulation and field test to explore the internal relationship between coal seam roof overburden failure and mine water inrush under mining disturbance.The failure law of coal seam roof overburden under“sandwich”hydrogeological conditions is clarified,and the development height of water flowing fractured zone is compared and analyzed by numerical simulation and field measurement.The main conclusions are as follows:（1）Through the analysis of the strata,lithology combination and spatial distribution characteristics of the mining area,it is obtained that the overlying water-filled aquifer of the minable coal seam in Longfeng Coal Mine is mainly the limestone water of the Upper Permian Changxing Formation+the Lower Triassic Yelang Formation,and the underlying water-filled aquifer is the limestone water of the Middle Permian Maokou Formation,which constitutes a“sandwich”hydrogeological condition of“overlying aquifer-minable coal seam-underlying aquifer”（2）The scanning electron microscope test was carried out on the coal seam roof samples.The test results showed that the primary cracks of all kinds of rocks in the overlying strata were not developed,indicating that the water conduction capacity of the primary cracks in the roof overlying rocks was weak,and the possibility of connecting the roof aquifer was small.The water channel of working face was mainly caused by the influence of coal seam mining.（3）According to the theory of’key stratum’,it is concluded that the key stratum of the overlying strata of No.9 coal seam roof is the fine sandstone at 3.00 m and 18.27 m in the upper part of the coal seam.The introduction of’beam structure’analysis shows that the key stratum will be broken and accompanied by the formation of water-conducting fissures during the continuous advancement of the working face,and the fissures will continue to develop upward,but the final development height needs to be determined.（4）The FLAC^3Dnumerical simulation method is used to analyze the vertical（5）displacement,vertical stress and plastic zone evolution of roof overburden under different advancing distance of working face.It is obtained that in the process of coal seam mining,the plastic failure zone is a typical"saddle"type,the maximum height of the plastic zone is 63m,and the change of stress and displacement in the vertical direction of overburden presents a trend of"rapid increase-slow increase".The vertical stress distribution of overlying rock shows that the middle is low and the ends are high.（6）The“high-density electrical method+borehole imager”detection technology was used to comprehensively detect the height of the water-conducting fissure zone in the 120905 mining face.The actual development height of the water-conducting fissure zone was 56m～68m,and the maximum height of the water-conducting fissure zone was 63m by the simulate calculation,which was within the range of the actual measured value,thus indicating that the method of"plastic zone"is reliable to analyze the evolution of water-conducting fracture,and the research results have reference significance for the height prediction and engineering measurement of water-conducting fracture zone under the"sandwich"hydrogeological conditions in the northern Guizhou coalfield.