Numerical Parametric Study of Settlement and Load Transfer Mechanism of Pile Group Due to Twin Stacked Tunnelling with Different Construction Sequences

Construction of tunnels in urban cities may induce excessive settlement and tilting of nearby existing pile foundations. In this study, numerical parametric study was conducted to investigate the influences of twin stacked tunnelling with different construction sequences on an existing (2 x 2) pile group. Twin stacked tunnelling was simulated one 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 (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 limited effect on induced pile group settlement, tilting, lateral deflection and load transfer mechanism. The computed cumulative pile group settlement was about 22% larger for tunnelling sequence TS than for tunnelling sequence TS.