Shear slide block theory and its control strategy for coal wall in deep roadways

Aiming at the problem of shear failure induced by the continuous large deformation of surrounding rock in the roadway of deep coal mine, a theoretical mechanical model of shear slide block in the surrounding rock of deep coal roadway was established,the safety factor of shear slide block was deduced,and the failure mechanism of shear slide block was revealed. The mathematical model of the safety factor of shear slide block was derived by the limit equilibrium analysis method. It was concluded that under the condition of the inherent mechanical properties of the coal body,the cohesive force has the greatest influence on the shear slider safety coefficient of the coal body of the roadway gang with a positive linear relationship. In external conditions,the safety factor decreases exponentially with the increase of roadway height. Based on the shear slider theory model,taking the deep coal roadway in the Chengjiao coal mine as the research background, the UDEC software was used to analyze the influence of roadway height, cohesive force, joint and fracture, and support mode on shear slide block motion. The results show that:① The conjugate shear surface appears after mining on both sides of roadway,forming shear slide block motion. The higher the roadway height,the smaller the cohesion,and the more unstable the roadway. ② For joints development roadway,the damage of the hanging wall is larger than that of the footwall. The larger the dip angle,the greater the bulge of the roadway side. When the joint dip angle is 65°,the displacement of the shear sliding block in the side reaches 0.78 m. The middle and lower part of the crack is open,and it is easy to shear the bolt when using the bolt support,resulting in the bolt failure. ③ After the side cable is used,the crack opening is effectively restrained and the anchoring effect of the bolt is played normally. Compared with the support with ordinary anchor cable and without support,the protrusion of the side wall with cracks is only 0.14 m,which is reduced by 83.1% and 75.4% respectively. It is proved that adding cable anchor cable has a better control effect on the wall rock of the side wall. In view of the field situation and combined with the shear slider model,a collaborative control strategy of "crack prevention-clearance reduction-slip prevention" was proposed. i. e. the surface layer and shallow part are supported by using high strength pre-stressed anchor rod,anchor cable and metal net component reinforcement to prevent the crack of surrounding rock,the deep part is supported by using wall rock modification technology to reduce cracks,and the local serious instability part is supported by side cable to suppress shear sliding block movement. In the fractured surrounding rock of coal roadway,it forms a composite bearing structure,which effectively control the deep coal roadway surrounding rock deformation. The research results provide beneficial reference for the stability control of surrounding rock of deep coal roadway.