Regional distribution law of water-conducting fractured zone height in high-strength mining of thick and extra-thick coal seams in China

The measured data of the height of water-conducting fractured zone under fully-mechanized top-coal caving and large mining height fully-mechanized mining of thick and extra-thick coal seams in China were collected. A total of 179 groups were collected,including 51 groups of hard overlying rocks,100 groups of medium-hard overlying rocks and 28 groups of soft overlying rocks. On this basis of the distribution of the 14 major coal bases in China,the height of the water-conducting fracture zone and the range of the fracture-mining ratio under different overlying rock types were listed,and the height distribution map of the water-conducting fracture zone China’s coal mines was drawn. Based on the regression of the predicted formula for the height of the water-conducting fracture zone (referred to as “crack height”),the distribution characteristics and main influencing factors of the height of the water-conducting fracture zone in three typical mining areas were analyzed,as well as the differences between the measured water-conducting fracture zone height data. The following research results were obtained:from a national perspective,the measured average fracture-mining ratio increases with the lithology from soft,medium-hard to hard,and the average fracture height value of hard overlying rock is 1.52 times and 2.29 times that of medium-hard overlying rocks and soft overlying rocks,respectively. The average crack height of medium-hard overlying rock is 1.5 times that of soft overlying rocks; the height of water-conducting fracture zones of different overburden lithologies increases with the increase of mining thickness,and the rate of increase under hard rock conditions is significantly higher than that of medium and weak overlying rocks; the fracture mining ratio decreases with the increase of mining thickness,and the decreasing rate tends to stable with the mining thickness reaching a certain thickness. The Huanglong-Binchang Mining Area of Huanglong Base belongs to the type of medium-hard covered rock,and the height and fracture ratio of the water guide fracture belt are significantly higher than the mining area of eastern China. When the working face length is more than 170 m,the development height of the water-conducting fracture zone is affected by the working face length.Its height and fracture-to-mining ratio increase with the increase of the working face length. Jalainuoer mining area of the Eastern Mongolia (Northeast)Base belongs to the extremely weak type of overlying rock. For this type of overlying rock,according to the long-term practical data of the development height of the water-conducting fracture zone,the minimum fracture-mining ratio is only 5,and when the mining thickness reaches 16 m,it is only 68% of the national average fracture-mining ratio of soft overlying rock,and a trend of adoption is proposed to predict the development height of water diversion crack zone under the extremely weak rock cover condition. The shallow buried mining area of Shendong Base has the characteristics of shallow buried depth,thin bedrock,thick soil layer,and high-intensity mining. The measured heights of the water-conducting fracture zones are very different,and the fracture -mining ratio is concentrated in the range of 19 to 28,and the maximum is 35,which is significantly higher than the fracture-mining ratio of the hard clad rock conditions in the country,especially in the eastern mining areas;.However,in some mines,the occurrence of thick laterite layers has a significant inhibitory effect on the development of water-conducting fracture zones. The measured fracture-mining ratio is 7.16 to 7.78,which is still 15% to 53% lower than that of mining under similar soft roof conditions. The prediction formula of water-conducting fracture zone obtained by regression of measured data has good applicability,which can provide a basis for height calculation of water-conducting fractured zone in the high-strength mining of thick and extra-thick coal seams under the conditions of different overburden types in China.