Elastic analysis of tunnelling beneath capped pile groups

Abstract

The response of pile groups to ground movements caused by tunnelling has received little attention by researchers for cases involving capped pile groups and tunnel-pile clashes. In this paper, tunnel- pile group interaction (TPGI) is studied using a linear elastic continuum-based finite element model. In the analysis, piles are modelled as Euler-Bernoulli beams that are either constrained by an elevated cap or have a free-head condition; the soil is modelled as an elastic continuum. In the first part of the paper, two pile groups with a 2 x 2 and a 3 x 3 configuration, respectively, are considered for both the cases of tunnelling adjacent to and beneath the piles. The displacements and internal forces of the piles are evaluated, as well as the foundation response in terms of cap movement for varying tunnel-pile group horizontal offset. The effects of increasing the tunnel depth on the TPGI are also evaluated. In the second part of the paper, the impact of tunnel-pile clash on pile settlements and post-tunnelling forces along the trimmed piles is studied for varying cap stiffness. It is shown that the outcomes of the proposed model compare well with more rigorous numerical analyses, hence suggesting the viability of the model as a reliable preliminary design tool.