Engineering characteristics and deformation control of roadways in fractured rock mass

The mining conditions of underground coal mines are complex. The development degree of surrounding rock fissures of underground roadways is high, significantly affecting roadways' stability and making a large number of them difficult to maintain. To further study the engineering characteristics of fractured rock roadway and put forward corresponding control measures, the deformation and failure characteristics of fractured rock roadway and typical supporting structure are analyzed based on field investigation and theoretical research. The fracture development in the coal mine is investigated and counted using three line discontinuity measurement method. The discrete fracture network (DFN) is used to reconstruct and restore the fractures obtained from on-site survey in FLAC3D. After comparing with the field monitoring data, it is considered that the fracture reconstruction model can be used as a qualitative reference for the comparison of the effects of different support methods in support design. The deformation and fracture characteristics of typical fractured roadway surrounding rock in some southern China mining areas are analyzed. Five control points of fractured rock mass are put forward, including improving the initial support stiffness and strength of the support system, making full use of the bearing function of deep stable rock mass, expanding the bearing area of the support system, accurately grasping the necessary support stiffness of the support system, especially the passive support and active support, and effectively improving the integrity and bearing strength of fractured rock mass. Using the bearing theory of superimposed compression arch, a combined control technology is proposed, which is based on the bearing system of "long-short" bolt (anchor cable) and the controlled grouting reinforcement of "internal-external" structure. Based on the numerical calculation, it is considered that the scheme can eliminate or reduce the tensile stress zone of the roadway surrounding rock, and effectively prevent the loose deformation caused by the tensile shear failure of the rock mass. Field tests were carried out at Mukong Coal Mine, Guizhou Province, China. The on-site monitoring data shows that the two sidewalls' approach distance is 0.1 m during the four-month observation period. The roof-floor's approach distance is 0.12 m. The final deformation rate is less than 0.2 mm/d, indicating that the support scheme of "long-short" anchor (anchor cable) combined with grouting reinforcement can effectively control the fractured rock roadway's large deformation. © 2021, Editorial Office of Journal of China Coal Society. All right reserved.