Variable Cross-section And Soft & Plastic Layers Crossover Subway Tunnel Construction Technology

When it is in the condition of abundant groundwater, weak stratum, large span, changeable section, and the top-building or the ground pipe is in great numbers that the subway construction process will be much more complex. Research on this problem is just begun in China at present. So the correlate theory gets behind of flourishing subway construction. Based on Nanjing NO.1 project Gulou-Xuwu subway practice, this paper focus on subway construction technology under great and changeable section, soft plastic-flow stratum condition. The main contents are as followings:1. Construction method is compared and elected to the subway structure which has large span and changeable section. Results show that it is better according to the section are, that is, the small section is firstly excavated firstly then the bigger one.2. Construction under soft flow-plastic stratum is simulated. Results indicate that it is effective on controlling the ground drop when adopting sidesteps method with shed advancing and injecting.3. The best construction parameters are acquired through elastic-plastic FEM numerical simulation after analyzing the displacement change in the process of subway excavation, and it can provide instruction for subway design and construction in similar instance.4. the ground and vault displacement are both in the range of control through monitoring data, and the rule that rock stress and lining internal force is 'sharp change-slowness change-stabilization'. The data shows that lining is appropriate, and construction measure is safety.The above research has been applied in practice and has received notable mechanic and social benefit, which also has important reference for similar subway.