Study on Height Development Characteristics of Water-Conducting Fracture Zone in Fully Mechanized Mining of Shallow Thick Coal Seam under Water

Abstract

The height of water-conducting fracture zone (HWCFZ) is one of the important technical parameters for water-preserved coal mining. The purpose of this paper is to acquire information about the height development characteristics of water-conducting fracture zone (WCFZ) in fully mechanized mining of shallow thick coal seam under water body in western mining area of China. The 91,105 fully mechanized mining face of Daheng coal mine under composite water body was taken as the research object, the development height, morphological characteristics, development and evolution process of WCFZ in working face mining were studied through underground up-hole water injection method by intervals, borehole TV and numerical simulation. The results show that the HWCFZ in 91,105 fully mechanized mining face is 52.7~53.6 m, and the fracture mining ratio is 12.55~12.76. The final development form is saddle-shaped with “large at both ends and small in the middle”. It is accurate and reliable to determine the development characteristics of overburden fractures and the HWCFZ by the field measurement of the combination of underground upward hole segmented water injection method and borehole TV. The development height of the water-conducting fracture zone obtained by numerical simulation is consistent with the field measured results. The development and evolution of the height of WCFZ presents four stages: “development–slow increase–sudden increase–stability”. When the WCFZ develops to a certain layer, the cracks generated by the weak strata in the fracture zone of overlying strata on the working face will automatically close with the advancement of the working face, resulting in “bridging phenomenon”, which inhibits the further development of the WCFZ. That is, the existence of soft rock with a certain thickness in overburden will become the key inhibiting layer for the development of WCFZ, effectively blocking the communication between water-conducting fracture and overlying aquifer. The research results are intended to provide guidance for the implementation of water preserving mining and ecological environment protection in ecologically fragile areas in western China.