Stability analysis and control strategy of weakly cemented layered floor in mining affected roadway

In order to overcome the problem of asymmetry deformation and instability of the weakly cemented layered floor roadway under the influence of strong mining effect, the site investigation, theoretical calculation, numerical analysis, and engineering test methods are comprehensively adopted. Taking the auxiliary haulage roadway of the working face in the Meihuajing Coal Mine in China as the engineering background, the deformation and failure mechanism of roadway surrounding rock and the control measures are studied. The results show that the coal-bearing rock series in the mine field have low diagenesis degree, poor cementation degree, and well-developed bedding in the roof and floor strata. Therefore, the roadway surrounding rock has a tendency to produce large deformation. Under the mining influence, the roadway exhibits significant asymmetric deformation and failure. The shoulder corner on the solid coal side, the bottom corner and floor on the coal pillar side are concentrated areas with large deformation, and the roadway convergence is mainly manifested by the floor heave. Due to the dynamics of the position of the working face and the creep of the weakly cemented soft rocks, the floor heave has typical time and space characteristics. Based on the elastic theory, a transverse isotropic floor mechanical analysis model under the influence of mining is established, and the true stress state at any point of the layered floor is derived, which accurately reflects the asymmetric stress distribution characteristics of the layered floor. According to the Mohr-Coulomb criterion, the failure criterion of the layered floor is obtained, and the asymmetric saddle-shaped failure form of the floor is calculated by Matlab. The eccentric loading effect caused by the rotation of the key rock blocks in the overburden layer deflects the direction of the principal stress of the roadway surrounding rock. The larger the deflection angle of the principal stress, the more significant the asymmetry expansion of the plastic zone. Surrounding rock failure has significant directionality, and the damage degree of surrounding rock is greater in the direction perpendicular to the maximum principal stress. Aiming at the asymmetric failure characteristics of the strong mining induced and weakly cemented layered floor, a differentiated support technology for the floor based on the repair of the broken zone, the reinforcement of the plastic zone, and the bearing of the elastic zone is proposed. Engineering practice shows that the support system is well adapted to the asymmetric stress environment of the surrounding rock, and the deformation of the surrounding rock is effectively controlled. © 2020, Editorial Office of Journal of China Coal Society. All right reserved.