关键词: 深埋隧洞, 软岩大变形, 三维有限元-离散元耦合方法, 注浆加固

Abstract: Large-deformation hazards induced by excavation unloading in deep tunnels involve complex discontinuous behaviors, including crack propagation, rock mass fragmentation, and block rotation and squeezing. Owing to the assumption of continuous deformation compatibility, conventional continuum methods struggle to capture discrete kinematic characteristics, such as large-displacement sliding and rotation of rock masses after failure, and therefore cannot accurately reveal the mechanisms underlying bulking-induced large deformation. To investigate the three-dimensional （3D） discontinuous failure mechanisms under different rock mass deterioration conditions and the effects of reinforcement on structural reconstruction, a refined numerical model of quasi-static deep-tunnel excavation is established using the 3D combined finite-discrete element method. An improved insitu stress initialization approach and a dual-softening algorithm for the core material are incorporated into the model. Based on the TBM8-1 single-shield section of the water conveyance tunnel in the Yangtze River-to-Han River Water Diversion Project, the fracture evolution patterns of typical soft rock and extremely deteriorated soft rock under unsupported conditions are comparatively simulated. The effects of different pre-grouting parameters on the reconstruction of the load-bearing system are also quantitatively evaluated. The computational results demonstrate the following: (1) Under typical soft rock conditions, failure is dominated by rock mass fragmentation and squeezing, while the fragmented blocks maintain a stable deep-seated pressure arch through frictional interlocking. (2) When the surrounding rock is extremely deteriorated, the deep-seated pressure arch effect is significantly weakened or even lost, causing failure to develop into full-face collapse and instability. (3) Tunnel failure exhibits 3D spatial asymmetry and discontinuity, and the confinement provided by the tunnel face influences crack propagation paths. (4) Advance pre-grouting can constrain the movement of fractured blocks. Combining moderate-strength pre-grouting with deep sidewall reinforcement extending to a depth of at least one tunnel diameter promotes stress transfer to the deeper rock mass, reconstructs the pressure arch, and mitigates full-face bulking-induced large deformation in extremely fragmented soft rock.

Key words: deep tunnel, soft rock large deformation, three-dimensional finite-discrete element method, grouting reinforcement