Pile underpinning and removing technology of shield tunnels crossing through group pile foundations of road bridges

During the construction of Shanghai Metro line No. 10, the interval tunnel from Liyang Road Station to Quyang Road Station has to pass through the pile foundation of Shajinggang Bridge on Siping Road. Based on the survey of the existing bridge structure, surrounding environment, construction condition and working space, a proper construction scheme including pile underpinning with expanded raft and cutting pile directly with shield machine is proposed. In order to ensure the safety of bridge structure and the normal traffic capacity during the construction process, by means of the theoretical analysis and numerical simulation, the studies are carried out on reasonable excavation length of pile, load transfer mechanism of pile-raft system and the construction influence on bridge structure due to cutting pile, etc. The results show that the soil reinforcement and pile-raft underpinning can effectively reduce bridge settlement and improve the bridge loading state. Secondly, since the original load born by piles is mainly transferred to raft foundation, the residual part of the pile to be cut has little effect on the security of bridge structure. According to the field monitoring results, the settlement of bridge structure during the construction process is in good accordance with the calculated results, which indicates that the construction scheme is reasonable, the construction measures are appropriate and the bridge structure is in the allowable safety range.