Three-dimensional centrifuge modeling of the influence of side-by-side twin tunneling on a piled raft

Abstract

Although the effects of tunnel excavation on nearby existing pile foundations have been extensively studied, previous studies mainly focused on response of single piles and elevated pile groups. In this study, three-dimensional centrifuge model tests were carried out to investigate the effects of side by side twin tunneling on an existing two by two piled raft in dry sand. Upon completion of twin tunnel excavation, the measured cumulative settlement of piled raft due to tunneling near the pile toe is 2.7 times of that due to tunneling near the mid-depth of the pile shaft. For twin tunneling near the pile toe, differences of piled raft settlements due to each tunnel excavation are negligible. In contrast, settlement of piled raft due to the second tunneling is about 55% of that due to the first tunneling when twin tunnels are excavated near the mid-depth of the pile shaft. As an advancement of tunnel excavation near the pile toe, the axial loads carried by the front piles are decreased, and the decreased loads are transferred to the rear piles and the raft. On the contrary, twin tunneling at the mid-depth of the pile shaft causes a reduction in the front piles and raft, and the decreased loads are transferred to the rear piles. After completing tunnel excavation, the axial load carried by the raft is increased by 22.0% for tunneling near the pile toe, while it is decreased by 21.7% for tunneling near the pile shaft.