Characteristics of roof water hazard of coal seam in Huanglong Coalfield and key technologies for prevention and control

Huanglong Coalfield in Shaanxi is one of the main coal production bases in China. Coal mining is usually affected by the sandstone water of the thick Luohe Formation on the roof, resulting a significant difficulty in the prevention and control of water hazards. It is therefore of great importance to correctly analyze the characteristics of water inflow from the roof and successfully develop the key technologies for water hazard prevention and control, ensuring the safe production of coal mines. The types of roof water hazard and its main controlling factors were appropriately analyzed by collecting the information on water inflow at the working face of a typical coal mine. The variation of water inflow in the working face was identified. The formation mechanism of water hazard in the thick sandstone aquifer of the roof was then studied, and the key technologies were developed for the prevention and control of water hazard on the roof. The results show that: (1) Water filling in the roof aquifer of Huanglong Coalfield can be divided into 3 categories (the continuous water inflow, discontinuous water inflow and mud-sand burst) consisting of 6 types. Definitely, the continuous water inflow contains the controllable continuous type and the high-intensity continuous type. The discontinuous water inflow involves the separated layer water inflow (including the occasional and frequent types) and the pulsed water inflow. Besides, the mud-sand burst type is also included. (2) The form of water inflow in the roof is dependent on the thickness of the key aquiclude, the distance between the coal seam and the sandstone of Luohe Formation, and the water abundance of sandstone in Luohe Formation. Specifically, pulsed water inflow is likely to occur under the conditions of thin or little key aquiclude, weak water abundance of sandstone in Luohe Formation and small distance between sandstone and coal seam. Continuous water inflow will occur when the controlling conditions are thick key aquiclude that is distributed stably, medium to strong water abundance of sandstone in Luohe Formation and small distance between sandstone and coal seam. Separated layer water inflow will occur at a coalfield with very thick key aquiclude, weak water abundance of sandstone in Luohe Formation and very large distance between sandstone and coal seam. In addition, it is prone to form water-sand burst in case that poorly cemented geological bodies were developed in the Jurassic strata within the water-conducting fracture zone of the coal seam roof or roof fall appears in coal seams. (3) Successful water hazard prevention and control in Huanglong Coalfield needs the key techniques for monitoring and early warning of the groundwater level, separated layer water drainage by surface drilling, centralized water drainage through underground drainage tunnel, construction and maintenance of drainage systems, water-reducing mining, etc. In addition, the supporting management counter-measures for water hazard prevention and control include the fine management system of working face, daily analysis system of working face water situation, expert consultation, benchmarking learning system and so forth.