Stability analysis and control technology of surrounding rocks at deep large cross-section roadway

In view of the deformation and damage characteristics of the -760 m level large cross-section roadway in Xingdong Coal Mine, such as obvious subsidence of roof, sharp convergence of two sides, strong heave of floor, broken and loose of pillar wall of rock mass, the combined control technology of bolt-shotcrete-net-grouting, which integrates high strength anchor bolts (cables) support technology with multi-level interleaving, multi-layer concrete spray layer arch support, reinforcement arch with grouting behind segment and reinforcement by pouring concrete into the column wall, is put forward in this paper by methods of theoretical analysis, numerical simulation, engineering analogy and on-site observation. The combined support technology of bolting shotcrete and net injection analyzes the surrounding rock control mechanism of the specific support method of the deep large cross section intersection. The results shows that: ①when the boltsare installed more densely, the minimum thickness of the pressure arch formed by the superposition of compressive stress is greater, and the bearing capacity of the pressure arch is stronger;②when the bolt spacing is more than 700 mm, the maximum bearing capacity of the spray layer structure is less than 0.55 MPa. As the bolt spacing decreases to 400 mm, the bearing capacity of the sprayed layer increases and the spacing of the bolt show apower-like function growth relationship; ③the bearing capacity of the sprayed layer structure and the thickness of the shotcrete layer show a kind of “linear” relationship, that is, the bearing capacity of the spray layer structure has a linear relationship with the thickness of the sprayed layer; ④the numerical simulation results show that the area with the greater plastic failure depth of the surrounding rock is located at the top two shoulder sockets, and most of the plastic zone depth of the intersection is less than 2.4 m. When the length of the bolt is determined to be 2.4 m, the bolt can be anchored in the elastic zone of the rock mass. Based on the above research, combined with the on-site geological production conditions, the surrounding rock support scheme of the roadway intersection is determined, and the field engineering application is carried out. The field engineering practice shows that after the joint control technology of bolting shotcrete and net injection is applied,the maximum approaching distance between the top and bottom plates and the two sides are 166 and 134 mm respectively, and the maximum approaching rates are 9.8 and 7.3 mm/d respectively. The convergen cecondition of surrounding rock in roadway is good. The deformation of the surrounding rock at the intersection of the - 760 m level large section roadway is effectively controlled.