临江高承压水超深基坑开挖抗突涌分析与对策——以南京纬三路长江隧道梅子洲风井基坑为例

Analysis on and Countermeasures for Water Inrush in Construction of Ultra-deep Foundation Pit at Riverside under High Confined Water:Case Study on Deep Foundation Pit of Meizizhou Ventilation Shaft of Weisanlu River-crossing Tunnel in Nanjing

临江高承压水超深基坑的成功实施必须解决坑底突涌与抗浮安全两大关键问题。通过合理的施工工序设计确保围护结构与基坑安全,并为坑内主体结构施工提供安全的施工环境。结合南京市纬三路过江隧道梅子洲风井基坑,对该类复杂基坑的重难点问题进行分析,在支护结构、开挖方法、实施方案及施工工序等方面根据工程具体特点采取相应的技术对策,确定了采用水下开挖及水下混凝土封底的技术方案,并经计算分析确定了最优施工工序。梅子洲风井的实践经验表明:对开挖深度大、承压含水层厚度及埋深均极大而导致隔水帷幕难以穿透承压含水层的基坑工程,采用水下开挖方式可有效防止基底突涌的发生,并能改善围护结构的受力与变形状态;而水下封底混凝土的设置可承受坑底巨大的承压水压力,是确保工程实施的关键措施。

Water inrush and bottom floating must be avoided in the construction of ultra-deep foundation pits at riverside under high confined water.Therefore,rational construction procedure should be planned for such foundation pits so as to ensure the stability of the retaining structures and the foundation pits themselves and to provide safe conditions for the construction of the main structures in the foundation pits.In the paper,the construction of the foundation pit of Meizizhou ventilation shaft of Weisanlu river-crossing tunnel in Nanjing is studied.The challenges in the construction of the foundation pit are analyzed,technical countermeasures are taken in the aspects of retaining structure,excavation method,implementation plan and construction procedure,the technical scheme of underwater excavation and underwater bottom-sealing is adopted,and the optimum construction procedure is determined according to the calculation analysis results.Conclusions drawn are as follows：1）For ultra-deep foundation pits where the excavation depth and the confined aquifer thickness are so large that it is difficult for the waterproof curtain to penetrate the confined aquifer,the application of underwater excavation can effectively avoid water inrush and can improve the force and deformation state of the retaining structures;2）The underwater bottom-sealing concrete,which can bear the high pressure of the confined water,is the key to the successful implementation of the project.