A CENTRIFUGE MODEL STUDY ON PILE GROUP RESPONSE TO ADJACENT TUNNELING IN SAND

摘要

In urban areas, there are inevitable interactions between existing structures and new constructions such as tunneling. A series of centrifuge model tests has been carried out to study the effects of tunnelling-induced soil movements on the adjacent pile group in sand. The tunneling process was simulated by reducing the diameter of the model tunnel for various ground loss values in 100g centrifugal acceleration. The tunneling machine is a mechanical type that can reduce diameter in co-axial direction to create a clear boundary condition. Two model pile groups consisting of four piles each with different lengths were embedded in dry sand at either side of the tunnel. The effects of horizontal distance between the pile and tunnel center (X_(p) ), relative pile tip position to the tunnel center (Z_(pe) ), vertical loads on the pile groups, and cover depth ratio (C/D ) were investigated in this study. Zones of influence were applied to investigate the area of large soil movements with the adjacent pile group. For small ground loss ratio (ΔV/V _(0)), the pile group movements increased almost proportionally to ΔV/V _(0). While for the large ΔV/V _(0) over 3%, the pile movement increment gradually decreased with ΔV/V _(0), except for the pile group with the front pile resting in the large displacement zone, of which movement still proportionally increased with ΔV/V _(0). The effect of X_(p) and Z_(pe) on the pile cap movement could be reasonably combined with the relative depth from the boundary of the less-movement zone to the pile length. Relative pile depth in the less displacement zone to the pile length and the horizontal position are the critical controlling factors of the profiles of pile bending moment and axial force.