Three-dimensional centrifuge modelling of the effects of twin tunnelling on an existing pile

Abstract

Tunnelling activity inevitably induces soil stress changes and ground deformation, which may affect nearby existing pile foundations. Although a number of studies have been carried out to investigate the effects of tunnelling on existing piles, the excavation of only one tunnel is often considered. The fundamental interaction between twin tunnel construction and an existing pile foundation has not been thoroughly studied. In this study, a series of three-dimensional centrifuge model tests investigating the effects of twin tunnel construction on an existing single pile in dry sand were conducted. The influence of the depth of each tunnel relative to the pile was investigated by constructing the twin tunnels either close to the mid-depth of the pile shaft or near the pile toe. The pile settlement induced by the excavation of the twin tunnels is found to be closely related to the depth of each tunnel relative to the pile. The measured cumulative pile settlement due to tunnelling near the toe is about 2.2 times of that due to tunnelling near the mid-depth of the pile shaft. Apparent losses of pile capacity of 36% and 20% are identified due to the construction of twin tunnels near the pile toe and at the mid-depth of the pile, respectively. Although there is an increase in the axial force induced in the pile when a tunnel is constructed at the mid-depth of the pile, significant increases in bending moment is not observed in any of the tests.