Research on key parameters of roof cutting and roadway retaining and roadway retaining technology in extremely close range coal seams

Aiming at the problems of difficult control of surrounding rock and easy failure of roof reinforcement support caused by the influence of overlying goaf in the mining of extremely close range lower coal seam, this paper takes the 90104 transportation gateway of a mine in Shanxi as the research object, carries out the key parameter analysis and roadway retaining technology research of roof cutting and roadway retaining in extremely close range coal seam, establishes the roof cantilever beam structure model of roof cutting and roadway retaining in extremely close range coal seam, and obtains the surrounding rock structure characteristics and roof cutting and pressure relief technology principle of roof cutting and roadway retaining in extremely close distance coal seam. Through theoretical calculation and analysis, it is determined that the maximum roof cutting height of the 90104 transport gateway is 5.7 m, the roof cutting angle is 15°, and the roof cutting hole spacing is 0.65 m. In view of the problems that the roof support of the retained roadway is easy to fail, and the coal side is prone to spalling and damage, the anchor cable is used to reinforce the support design of the coal side of the retained roadway. According to the characteristics of deformation zoning, the retained roadway is divided into advanced support area, severe roof deformation area, slight roof deformation area and roadway stability area, and the targeted support scheme designs are given: the advance support area uses a single pillar and a hinged beam to support the advance support; the severe roof deformation area adopts the method of one beam and four columns to strengthen the support; the single prop and π-type roof beam are gradually withdrawn in the slight roof deformation area and the roadway stability area. The retaining gangue support design and spray layer design are carried out in the retaining section, and a complete set of technical scheme for roof cutting and roadway retaining in extremely close range coal seam is formed. The field engineering practice and monitoring results show that the maximum displacement of the roof of the 90104 transportation gateway is 120.1 mm, and the maximum displacement of the side is 165.3 mm. The maximum stress of the top and side anchor cables is 204.3 kN and 227.3 kN, which are 34.9% and 48.6% higher than the initial stress, respectively. The deformation of the roadway and the increase of the stress of the anchor cable are within a reasonable range. The whole roadway is relatively stable and no instability occurs. The bearing capacity of the support system is normal, and the control effect of the surrounding rock of the roof cutting and roadway retaining is good, which provides a reference for mining under similar extremely close conditions.