Centrifuge and numerical modelling of stress transfer mechanisms and settlement of pile group due to twin stacked tunnelling with different construction sequences

摘要

This study reports a series of centrifuge model tests, aiming at investigating the effects of construction sequence of twin stacked tunnels advancement on an existing pile group under working load in dry sand. Twin stacked tunnelling was simulated after the other with the first tunnel excavated near the mid-depth of the pile shaft and the second either next to the toe of the pile (test ST) or below the pile (test SB). In addition, two tests were performed with change of construction sequence of twin stacked tunnels (i.e. tests TS and BS). The first tunnel was excavated either near the pile toe (test TS) or below the pile (test BS) and second tunnel near the mid-depth of the pile shaft. The centrifuge tests were back-analysed by three-dimensional finite element analyses using a hypoplastic model, which takes strain-dependent and path-dependent soil stiffness into account. The measured and computed results have revealed that change of twin stacked tunnels construction sequence had substantial effects on pile group settlement, pile cap tilting and lateral movement in the pile group. In contrast, no significant effect was found on induced bending moment and load transfer mechanism in the piles.