The influence of pile group loading on existing tunnels

In the urban environment the influence of pile group loading on existing tunnels is a common problem. Consequently, over the past 30 years tunnel owners have developed restrictive guidelines for the construction and loading of piles in the vicinity of their tunnels. These guidelines are based on experience. This paper assesses the influence of pile group loading on existing tunnels using the finite-element method with the aim of improving the current restrictive guidelines. In the first part of the paper 3-D analyses are used to justify a 2-D plane strain approach to analyse the loading of pile rows. This approach is then used to analyse the response of a tunnel to loading of piles located either on both sides (case A) or on one side (case B) of the tunnel. In all analyses the pile rows are wished-in-place, and the construction of individual piles is not considered. The results of these analyses are used to formulate design guidelines relating the clear distance between the pile rows and the tunnel to maximum allowable tunnel deformations both in terms of tunnel distortions and global movements.