Asymmetric failure and control measures of large cross-section entry roof with strong mining disturbance and fully-mechanized caving mining

Asymmetric deformation failure during the process of excavating and supporting of large cross-section entry roof with strong mining disturbance and fully-mechanized caving mining at Wangjialing coal mine was studied systematically through field investigation, laboratory test, analytical analysis, numerical simulation and in-sit test. The mechanism of deformation failure and the controlling measures were investigated. The roof of gob-side entry was found to display the asymmetric deformation failure characteristics, which included sever subsidence of roof near the pillar sides, radical horizontal dislocation deformation and dislocation, embedding, step convergence at the roof-wall corner, et al. The lateral main roof broke at a distance of 6-7 m away from the gob-edge above the pillar. Unbalanced side abutment q and rotary deformation pressure σ induced by the broken and rotation of main roof are the fundamental cause causing the asymmetric deformation failure characteristics. The deformation failure was significantly influenced by a key position of roof near the pillar side and roof-wall corner surrounding rocks. Due to the movement of the unstable overlying strata and the entry excavation, the surrounding rock structure and stress distribution were asymmetric evidently on the axis of roadway, but the original supporting systems did not provide the reinforced support to key position and adjust to the strongly horizontal dislocation, which resulted in the asymmetric strata behaviors shortly after the development of entry. The asymmetric failure tended to be more severe later affected by the extraction of the present panel. The control principle of the entry was analyzed and an asymmetric supporting system was proposed composed of cable-beam-net, asymmetric cable-beam and cable-truss. And the support scheme was put into field application. The numerical simulations and engineering applications demonstrated that the support weakened the asymmetric of stress and displacement of the roof and controlled the asymmetric deformation failure. © 2016, Science Press. All right reserved.