3D centrifuge and numerical modelling of lateral responses of a vertical loaded pile group to twin stacked tunnels

Tunnel excavations inevitably induce stress release and soil movement, which may affect the safety and serviceability of nearby existing pile foundations. The effects of tunnel construction on existing piles have been extensively investigated, but little attention was paid to lateral responses of piled foundations to tunnelling. In this study, a series of three-dimensional centrifuge model tests and numerical simulations using an advanced hypoplastic soil model were carried out to investigate the response of an existing vertically loaded 2 × 2 pile group in lateral direction due to advancement of twin stacked tunnels in dry sand. In each test, twin tunnelling was simulated three-dimensionally 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 group (test ST) or below but to one side of the pile group (test SB). In addition, influences of tunnel depths and locations with respect to pile group response are investigated. The most significant lateral movement of the pile cap induced after the twin tunnelling in each test. The induced bending moment and pile deflection can be critical on completion of twin tunnels in test ST. In spite of being vertically loaded pile group, the twin tunnelling caused lateral forces (shearing forces to the pile group) in each test. The calculation charts have revealed that the tunnel depth and location relative to the pile group significantly influence induced pile cap lateral displacement and pile head bending moment.