Division and practice of water-preserved mining in ultra-thick coal seam under ultra thick sandy conglomerate aquifer

Taking Cuimu coal mine in Yonglong mining area as research background,the spatial structure of aquifer ( separated) and coal seam and overburden features were analyzed. Then the exploratory results of development height of water-flowing fractured zone was analyzed,and the division and practical research of water-preserved mining in thick coal seam under great thick sandy conglomerate aquifer in the studied area was carried out. It is shown that the water conducting fractured zone height is 19. 93-23. 23 times to the extraction height,which has spread to the overlying Cre- taceous aquifer. The protective layer thickness of water-preserved mining is determined to be 30 m. Thus the studied area is divided into three zones,i. e. nature water conservation mining zone,controllable water conservation mining zone and water conservation limit mining area,and the corresponding water preserving mining methods are proposed ai- ming at each zone. Practices indicate that the effective ways of water conservation mining under great thick sandy grav- el aquifer mainly include controlling the development height of water conducting fractures,choosing the appropriate layout and speed of the working face,and recovering and reconstructing after the destruction of waterproof layer min- ing.