Objective Despite the complex geological conditions in Fuzhou region, multiple metro lines currently are cross the Minjiang River. It is therefore necessary to summarize experiences related to the soil instability treatment at shield tunnel excavation faces in riverbed fault zone strata.

Method Taking Fuzhou Metro Line 4 slurry shield tunneling through the riverbed fault zone strata beneath the Minjiang River as a case study, the project overview is introduced. The soil instability conditions of shield excavation face in fault zone strata are described, and the causes for incidents are analyzed. A treatment method combining filling of the shield machine slurry chamber with grouting reinforcement beneath the riverbed is adopted to address the soil instability at the excavation face. The treatment measures and their effectiveness are analyzed in detail.

Result & Conclusion  The extremely fractured and poorly stable rock mass at the intersection of two geological fault zones is the fundamental cause of excavation face instability and chamber collapse during shield tunneling. The reinforcement method of chamber filling combined with riverbed grouting is feasible, and the treatment of excavation face soil instability has achieved satisfactory results.