Design and analysis of retaining system of foundation pit of Qingchun Road River-Crossing Tunnel in Hangzhou

The Qingchun Road River-Crossing Tunnel in Hangzhou is the first tunnel that crosses beneath the famous Qiantang River. The pits at both the north and south sides are typically silt-based ones. The scale of the pits is very large and is the deepest pit in Hangzhou. In the pit at the north side, the retaining structures of SMW method plus steel support are mainly applied, among which the longest piles are up to 27 m. In the pit at the south side, the maximum excavation depth is 30 m, and the retaining structures of open cut plus underground diaphragm wall, open cut plus SMW method and steel support, open cut plus foundation reinforcement and open cut plus anchors-gunite-web shoring are used. It is the first time for the excavation to encounter the impact of high-pressure water in Hangzhou. The precipitation of tube wells supported by light wells and waterproof curtain walls successfully resolves the potential hazards posed by high-pressure water. According to the analysis of monitoring data of horizontal displacements, axial forces, surface settlements and water levels, some useful variations of the parameters are obtained, and they can be used as references for the design and construction of similar projects.