Continuous-discontinuous analysis of deformation failure mechanism and supporting effect of roadway in deep fractured rock mass

The deep fractured rock mass of Jinchuan No. 2 Mine has the remarkable characteristics of high-strength rock and low-strength rock mass. The surrounding rock shows significant large deformation behaviour, which frequently leads to the destruction of supporting structures, such as spray anchor net or lining and seriously, threatening the mining activities. Based on the field work in deep roadway of Jinchuan No. 2 Mine and the continuous-discontinuous numerical analysis method, this study discussed the large deformation mechanism and supporting effect. First, the field investigation reported that the surrounding rock had typical layered, fractured and mixed structure characteristics, and caving and bottom drum were typical failure mode. Next, based on laboratory tests, field monitoring data, the Voronoi-based breakable block model and the discrete fracture network model, the roadway excavation processes were simulated to capture the damage and fracture characteristics of surrounding rock. Finally, the support structure responses were simulated using the solid element and rockbolt element. The numerical results show that the spacing and dip angle of joints significantly influenced the location of stress relief zone and the formation of pressure arch, which results in deformation anisotropy and fracture heterogeneity. There were significant difference in limiting the deformation of surrounding rock for the supporting structures of rockbolt, spray layer+rockbolt and U-shaped steel arch+rockbolt. The rockbolt and lining could effectively restrain the caving zone and limit the displacement of top arch, but could not effectively restrain the floor uplift. The advance grouting, lengthening rockbolt and steel arch were important measures to control the large deformation. This study can provide theoretical support and practical guidance for deformation control and support design of roadway in deep fractured rock mass.