With the rapid development,subway construction is inevitable to pass through existing urban o-verpasses,which will significantly impact its settlement and stress state.This research relies on the under-pinning engineering of pile foundations of Jianhe bridge passed by Shijiazhuang Metro Line 2.Using finite element software,a three-dimensional finite element model is established,and the whole process of pile foundation underpinning is simulated.The settlement change rule is obtained through numerical calculation and compared with the field data.The results show that the settlement is large in the underpinning position of South Jianhe Bridge,in which the monitoring should be strengthened.Finally,the stress history of the special-shaped slab on the bridge deck and the pile foundation is analyzed,and the laws are as follows.The stress changes of the special-shaped slab on the bridge deck are mainly concentrated in the construc-tion stage of the pile breaking.In the whole process of underpinning construction,for the original pile,the forces show a change law of first decreasing and then increasing,while the effective stress of the newly-built pile foundation showed a continuous increase.The pile-breaking construction effectively transfers the force of the original pile foundation to the newly-built pile foundation,and shield construction has little effect on the stress state of each structure.The results can provide references for the design and construc-tion of similar underpinning projects of pile foundation.
special shaped slabpile foundation underpinningsubwaybridgeshield underpassfinite ele-ment method