Abstract: To resolve the stability control problem related to the fractured soft rock surrounding deep roadways, a case study is performed on the Xingdong Mine-980 roadway tunnel to investigate the characteristics and mechanism of the deformation and failure of the surrounding rock mass, with combining the procedures of field investigation, numerical simulation, in-situ testing and monitoring and so on. A bolt-shotcrete-net-grouting combined supporting system is developed, which is composed of densely distributed high-strength anchors, newly shotcrete protecting layer and time-lag grouting reinforcement. The controlling mechanism is explored for the surrounding rockmass stability with different types of supporting structures, and a numerical analysis is performed on the influence of bolt spacing and shotcrete layer thickness on the stress and displacement fields of the surrounding rockmass. It is shown that: 1) With the bolt spacing decreasing from 0.7 m to 0.3 m, the bearing capacities of anchor bearing arch and shotcrete layer structure increase following a power law, the compressive stress in the anchorage zone increases practically linearly and the displacement of surrounding rock decreases sharply; 2) When the shotcrete layer thickness increases, the bearing capacity of shotcrete layer structure increases linearly, similar to the compressive stress in anchorage zone; meanwhile, the displacement of surrounding rock decreases substantially; 3) When the layer thickness reaches 200 mm, compression prevails in most part of the surrounding rock without anchors, and the tensile stress zone shrinks significantly. Based on the above simulations, a supporting scheme is proposed and implemented for an experimental roadway with combining production and geological conditions. The field practice shows that bolt-shotcrete-net-grouting combined supporting technique can effectively control the large deformation of surrounding rock.

Key words: fractured soft rock roadway, high-strength shotcrete layer, shotcrete layer thickness, anchor distance