Instability Mechanism and Engineering Cases of the Surrounding Rock in Deep High Stress, Weak Strata Chambers

The surrounding rock of chambers under deep high stress conditions has the characteristics of a long deformation duration, large loosening range and large deformation. It is difficult to control chamber deformation with conventional support methods. The deformation and failure mechanism is as follows: strong creep of the weak rock in high stress conditions and gradual fracture of the support structures until support failure, and even roof collapse. On the basis of many years of engineering practice, this paper analyzes the strata pressure characteristics and instability mechanism of three typical pump chambers. The concept of the reconstructed bearing layer is proposed. These chambers include the −250 m pump chamber in Sino-Thai Company, 39 mining area pump chambers influenced by large faults in the Zhongmacun Coal Mine, and the −800 m pump chamber of the Zhaogu No. 2 Coal Mine. Combined with the reinforcement principle of the surrounding rock of chambers, a theory for rebuilding the bearing strata was proposed. Multiple supports on the basis of the New Austrian Law were suggested. As an example, multiple support technologies for the drainage pump chamber in the Zhaogu No. 2 Coal Mine were proposed. The primary support was combined with bolts, cables with high strength surface protection components. The secondary support of the surrounding rock was grouting, which can strengthen the strata. The third support was a double-deck I section rigid steel bracket. The fourth support was shotcrete, which can seal the strata. Field investigation showed that the surrounding rock of the drainage pump chamber was in a stable condition. The displacements of the walls, roof and floor were 28 mm and 5 mm, respectively, and the displacement rate was less than 0.2 mm per day. According to the usage situations of the three chambers, good technical and economic benefits have been achieved.