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  Super-large Diameter Slurry Shield Tunneling in Rock-Soil Mixed Ground under 0.72MPa Pressure: A Case Study of Nanjing Yangtze River (Weisan Road) Tunnel

  Nanjing Yangtze River (Weisan Road) tunnel is one of the most difficult shield tunnel project of the world, which has many special characteristics such as super-large diameter (14.93m), high water pressure (up to 0.72MPa), long distance tunneling (S-line:4140m, N-line:3557m), and complex geological conditions (including 400m rock-soil mixed ground with rock strength up to 115MPa). Key technologies for construction of shield tunnel are presented. Two new types of sealing structure were adopted for shallow cover, closely-spaced curve launching with large slope and curve arriving. Due to complex geological conditions, the cutting tools should be exchanged frequently. Based on laboratory tests and numerical analysis, special techniques were developed for stabilizing the tunnel face during hyperbaric intervention, in such a case, up to 92% of the tunnel face was supported by compressed air. A new system was designed for fast transportation of saturation diving shuttle in slurry shield, with face stability control technology, the largest (8606 mins) application of mixed-gas-saturation interventions were safely achieved with Max. overpressure 0.65MPa. In order to ensure the performance of tail seal in long distance tunneling, new grouting technology was developed for exchanging the tail seal in strongly permeable layer under 0.55MPa water pressure.

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