Investigation of effects of different construction sequences on settlement and load transfer mechanism of single pile due to twin stacked tunnelling

Construction of tunnels in urban cities may induce excessive settlement and tilting of nearby existing pile foundations. Various studies reported in the literature have investigated the tunnel-soil-pile interaction by means of field monitoring, centrifuge and numerical modelling, but the influence of construction sequence of twin stacked tunnelling on an existing pile is seldom reported in the literature. This paper presents a 3D coupled-consolidation numerical parametric analysis to understand settlement and load transfer mechanism in single pile due to twin stacked tunnelling with different construction sequences in stiff saturated clay. To accurately capture the tunnelling induced ground deformation, path- and strain-dependent soil stiffness at small strains were taken into account in each numerical analysis, by adopting an advanced hypoplastic clay model coupled with the inter-granular strain formulation. Twin stacked tunnelling was simulated one after the other with the first tunnel excavated near the mid-depth of the pile shift and the second either next to the toe of the pile (case ST) or below the pile (case SB). In addition, two more analyses were performed with change of construction sequence of twin stacked tunnels (i.e. cases TS and BS). The first tunnel was excavated either near the pile toe (case TS) or below the pile (case BS) and second tunnel near the mid-depth of the pile shaft. The different construction sequence of twin stacked tunnels at different depth had a substantial effect on induced pile deflection and settlement. In contrast, no significant effect was found on load transfer mechanism in the pile due to the change in construction sequence of tunnels.