Fracture characteristic and support effect around deep lined tunnels using CGP-FDEM simulation and field investigation analysis

The lining is one of the main methods of support and is chosen as the primary support for composite and reinforced roadways during mining excavation. Systematic investigations into the supportive effect of lined roadways in deep weak rock masses are highly desirable to improve support design and enhance roadway stability. The fracture characteristics and deformation are more prominent in the lining failure and damage to the surrounding rock. For investigations into the fracture mode and failure characteristics of the lining support, this study proposed a lining element support model in the graphics processing units (GPU) parallel combined finitediscrete element method (FDEM) program using compute unified device architecture (CUDA), referred to as CGPFDEM. The lining element model and excavation simulation method are implemented in the CGP-FDEM aim of simulation large-scale rock fractures in underground excavations. On this basis, the simulation of deep roadway excavation is performed under various support conditions, including low-strength and high-strength shotcrete, steel arch, and U-profile yieldable steel. Further, a comparative analysis is conducted between the field investigation and simulation results, focusing on fracture-fragmentation and large deformation of the surrounding rock, as well as the failure and fracture mode of the lining elements. Results of individual support effects indicate that the reinforcement conditions mainly affect the excavation damaged zone (EDZ) and the deformation of the surrounding rock. Rock fragmentation and buckling intensify the large deformation and instability of the roadway. Fracture evolution and instability of the surrounding rock can easily occur in weak areas due to severe stress concentration and the accumulation and release of energy. Based on the analysis, the principle of "uniform reinforcement of reactive force throughout the entire section" is proposed to alleviate stress concentrations and maintain the overall stability of the excavation space.