Deformation control of surrounding rocks of mining roadway indeep and close lower coal seam

Pingdingshan mining area Wu group coal and Ji group coal coal are (extremely) close coal seams, the distance between the seams is 2-15m, the distance between the group Wu coal seam and the group Ji coal seam is about 180 m, and the thickness of the overburden is 700-1000 m. Because of the large overburden depth, the concentrated stress of the coal pillars left over from the upper coal seam and the impact of multiple working face mining, the surrounding rock of the roadway has complex stress distribution, high stress level with poor anchorage, so it is prone to have large deformations, and the investment and maintenance costs are also quite high. In order to solve the problem that the stress distribution of surrounding rock of the mining roadway in the deep and close lower coal seam is complicated and the roadway support is difficult due to the influence of multiple mining, the stress distribution of the surrounding rock and the roadway deformation characteristics of the Ji15-31010 transportation roadway affected by mining were systematically analyzed. During the upper coal seam mining process, the peak vertical stress of the surrounding rock of the roadway was 18.72% higher than that of the lower coal seam, and the roadway surface displacement increased significantly. The maximum range of the two sides of the plastic zone is 3 m, and the maximum range of the roof plastic zone is 1.5 m. Based on the principle of reducing the stress of the surrounding rock and increasing the strength of the support, a dynamic three-dimensional support strategy with "unloading-yielding-resisting" as the core was proposed, and the roof of the roadway was designed to use ultra-high-strength yieldable bolt + steel mesh + M-shaped steel belt + the anchor cable and the ribs adopted the combined support of the same strong resin anchor bolt + steel mesh + steel ladder beam + anchor cable with the overall plan of stress relief in the surrounding rock stress concentration area or key parts. The single strand steel was used between the anchor cables and the strands were connected to form a three-dimensional integrity, which supported the shallow and deep, horizontal and vertical parts of the surrounding rock of the roadway in all directions. The pressure relief of blasting released the initial deformation pressure of the surrounding rock to allow the compression anchor to relieve the load on the supporting structure. This scheme effectively transferred the concentrated stress of the surrounding rock of the roadway from 2.5 m away from the surface of the roadway to the depth of the surrounding rock at 8.0 m away from the surface of the roadway. The industrial test results of this scheme show that the two sides of the roadway move closer to each other when the upper seam is mined. The maximum distance between the roof and floor is 230 mm, and the maximum displacement of the roof and floor is 156 mm. When mining the lower coal seam, the maximum displacement of the two sides of the roadway is 335 mm, and the maximum displacement of the roof and floor is 230 mm. The support effect of the roadway is good, and the deformation of the surrounding rock of the roadway can be effectively controlled, which can provide reference for the surrounding rock control of mining roadway under similar conditions.