Efficiency of pile barriers to mitigate supported excavation effects on existing tunnels

Abstract

This paper shows a numerical study to evaluate the efficiency of different schemes of pile row barriers to mitigate the risk due to a deep excavation in soft soils adjacent to an existing tunnel, then use numerical analyses to understand the main mechanisms of excavation-barrier-tunnel interaction. Three-dimensional FDM analysis was conducted on deep-covered and shallow-covered tunnels with different support structures, including pile barrier, twin retaining wall, anchor-pile barrier supporting structure, along with monitoring data from a case history in Wuhan, the Huazhong Science and Technology Park basement. The monitoring data show successful excavation and basement construction within allowable displacement thresholds in the presence of the barrier. Numerical results indicate that the twin retaining wall can effectively control lateral displacements of front and rear rows, leading to a substantial reduction in ground surface movements, thus, there is a great percentage reduction in horizontal displacements and settlement of the existing tunnel. While pile barriers with prestressed anchor cables show greater control over settlement than horizontal displacement of the shallow-covered tunnel. The results of the analyses permit to recognise the efficiency and mechanism of different protective barrier schemes, providing some guidance for a rational design of the intervention.