Investigation on tunnel responses due to adjacent loaded pile by 3D finite element analysis

Abstract

Underground structures are popularly utilized in urban development, especially tunnels for both transportation and utilities. The interaction problem between existing tunnel and piles from new constructed structures thus becomes unavoidable in dense population area. The tunnel loses its stability if the additional forces and changed diameters (due to adjacent piles under loading) of tunnel lining are drastically high. This depends on many factors, such as the clearance and pile tip level with respect to tunnel position. For preliminary assessment during the first stage of design, it is necessary to estimate this impact. The concept of tunnel protection zone is commonly adopted. However, to establish the tunnel protection zone for adjacent loaded pile, the understanding on this interaction problem is essential. This study analyzes the effect of adjacent pile under loading on the existing tunnel by 3D finite element method. The case study is the tunnel of MRTA project subjected to an adjacent 1 m bored pile under loading with various lengths and clearances. The additional forces (bending moment and axial force) and the tunnel deformations are investigated. The results show that the additional forces and the tunnel deformations decrease when the clearance increase and become insignificantly increasing when the clearance is larger than 3.5 m. The distribution patterns of additional forces and tunnel deformation are similar.