Discussion on roof water loss control method of coal seam based on pre-splitting grouting reformation(P-G)

In view of the technical requirements of roof water disaster prevention and water resources collaborative protection faced by coal mining in western coal mining area, this paper puts forward a technical idea of roof water loss control based on pre-splitting grouting reformation(P-G) according to the strain strength theory of material mechanics and the statistical results of mining fracture zones of different overburden types. The basic principle is that the continuous bedrock layer will be fractured into discontinuous rock layers by fracturing technology, and by weakening the “tip effect” of upward expansion of mining induced water flowing fracture in hard rock stratum to restrain the development height of water flowing fracture. Then, the soft clay grouting materials are used to modify the strata into relatively weak ones. Therefore, the P-G method plays a dual role in restraining the upward development of the water flowing fracture zone and reducing the water conductivity of the overlying strata, so as to realize the water loss control of the coal seam roof aquifer. Taking the Yushen Mining Area in the energy base of northern Shaanxi as the analysis object, this paper discusses the control method of P-G water loss in roof aquifer before mining, including the analysis of geological and hydrogeological conditions, the identification of water inflow(loss) pattern of aquifer in coal working face, prediction of development height of water flowing fracture zone, water gushing mode of overburden rock, determination of P-G time, horizon and time, horizontal hole hydraulic fracturing of roof strata and grouting modification. It has certain reference significance for roof water disaster prevention and water resources coordinated protection technology practice in Yushen Mining Area of the energy base in northern Shaanxi.