Main influencing factors for regional pre-grouting technology of water hazard treatment in coal seam floor and efficient hole arrangement

Regional advance grouting transformation and reinforcement of water conducting formation and aquifer is the main technical means to prevent and control the karst water hazards in the coal seam floor of North China type coalfields. Herein, analysis was conducted for the general application mode of the regional advance grouting transformation and reinforcement for water hazard treatment in the thin and thick limestone layers in the coal seam floor based on the basic mine hydrogeological principle of the application of regional advance grouting transformation technology. In the analysis, consideration was given to the hydrogeological structure of the coal seam floor, the influence of mining activities, the directional drilling hole, the grout diffusion capacity, and the boundary conditions of the grouting rock layer. Besides, analysis was also performed from the aspects of geological conditions of grouting rock stratum, grouting materials, grouting technology, etc. Thus, the main factors affecting the regional advance grouting treatment effect of karst water hazard in the coal seam floor were obtained, including the connectivity, openness, roughness and pore water bearing capacity of the grouting layer, the granularity, viscosity, time variation and firmness of grouting materials, and the grouting pressure, spatial layout of drilling holes, grouting methods, etc. In addition, according to the calculation formula of effective grouting pressure, the grout is inhibited by the comprehensive resistance of the borehole and the rock stratum gap during its flow in the borehole and fissure. As a result, the effective grouting pressure in the horizontal hole gradually decreases, which is easy to form a “cone” grout diffusion range. Finally, in view of the current commonly-used pattern of parallel arrangement of branch holes in horizontal section of regional advance grouting holes, the blind area between grouting holes may be caused by the excessive spacing and the attenuation of effective grouting pressure. Therefore, 3 types of efficient hole arrangement modes, such as the long-distance staggered parallel branch hole, the long-distance reverse complementary arc branch hole and short-distance feathery branch hole, were proposed according to the attenuation law of effective grouting pressure and grout diffusion range in the horizontal section of grouting holes, so as to eliminate the blind area of grouting. Hence, a basis could be provided for the scientific application of high efficient regional technology for water hazard treatment in the coal seam floor in advance.