Abstract:

Implementing the innovative "host shield+spray anchor support" open tunnel boring machine(TBM) in Guangzhou′s #4 tunnel for the Beijing water diversion project resulted in the collapse of fault and fracture zones. Consequently, considering the collapse characteristics and open TBM, a targeted treatment plan is proposed. This plan involves chemical grouting to fill collapsed cavities, reinforcing loose bodies, spray anchor support, dense arch support, and advance grouting reinforcement. A finite element numerical simulation model is established based on onsite conditions to assess the plan′s feasibility. The simulation results are: (1) The fault center experiences a maximum vertical displacement of approximately 2.1 mm, with a relative convergence displacement of the arch foot of 0.05%. (2) Shotcrete′s maximum tensile stress is approximately 1.0 MPa, and the bolt at the crown has a maximum tensile stress of 41.6 kN, which meets the stress and deformation control requirements. The applied chemical grouting effectively prevents further largescale collapses of the support structure. Reinforcement grouting successfully cements loose bodies, forming a 3 mthick bearing ring and preventing continuous collapse of the stone slag. After treatment, the primary support is substantially enhanced. The surrounding rocks not yet detached from the shield tail are pregrouted and reinforced, ensuring successful TBM passage through the fault and fracture zone. The measured maximum vertical displacement of the arch crown is approximately 2.0 mm, with a relative convergence displacement of approximately 0.10%, ensuring construction safety in the open section behind the TBM shield tail.This approach guarantees structural integrity and safety in challenging fault and fracture zones.

Key words: fault and fracture zone, collapse treatment, chemical grouting, numerical simulation, field monitoring, TBM tunnel