Behavior of up-lift pile foundation during large-scale deep excavation

Soil unloading and rebound induced by large-scale deep excavation may affect the performance and integrity of existing piles inside the excavation zone,especially for up-lift piles.The non-linear finite element is employed to investigate the behavior of the up-lift piles in Shanghai Expo Underground Substation Project during deep excavation.Parameters of the subsoil are obtained by inverse analysis of the load tests on the up-lift piles.The behavior of the up-lift piles during deep excavation and under normal working load is analyzed by using the parameters.Results show that the tension force induced by excavation exerts a more negative influence on up-lift piles than normal piles.Therefore this pretension should be taken into consideration during pile design.Analysis shows the bottom-enlarged up-lift piles are subjected to a larger pretension force during excavation than ordinary up-lift piles.The pretension force of piles under working load can be deduced from the combination of the tension force induced by excavation and the tension force induced by working load.