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.