Optimization of design parameters of displacement isolation piles constructed between a high-speed railway bridge and a double-line metro tunnel: From the view point of vibration isolation effect

Abstract

A double-line metro tunnel was constructed beneath an existing high-speed railway bridge in a city of east China. To avoid the unexpected displacement of the bridge resulting from the shield tunneling, the displacement isolation piles were employed between the shield tunnels and the pile foundation of the bridge. An accompanied optimization design issue of the isolation piles is analyzed in this work. The optimization target is not only that the displacement criteria of the bridge pile foundation during tunneling process must be met, but also an outstanding vibration mitigation effect in operation process should be achieved. In this work, a steady-state finite element analysis (FEA) is employed to evaluate the limit of the pile spacing according to the displacement criteria of the high-speed bridge. After that an analytical model and a three-dimensional (3D) finite-infinite element model of the bridge-foundation-tunnel system are established, respectively, for further optimization of the pile parameters from the view point of vibration isolation effect. The optimized pile spacing of the isolation piles for the real project case is finally recommended based on in-situ measurement data and the evaluation results.