Numerical insight into twin tunnelling-induced soil-structure interaction in battered pile-supported systems under lateral loading

With rapid increasing urbanization, the construction of twin tunnels adjacent to existing foundations has become common in underground development projects. This study investigates the influence of twin parallel tunnelling on elevated battered pile group and battered piled raft subjected to lateral loading in soft clay. A series of three-dimensional coupled consolidation finite element analyses, incorporating an advanced hypoplastic clay model with small-strain stiffness are carried out. The model parameters are validated using centrifuge test data to ensure realistic simulation of tunnelling-induced ground deformations. Twin tunnels are positioned at varying depths relative to the battered piled foundation: neat the shaft, near the toe, and below the toe of the piles. Results reveal that the largest lateral displacements and differential settlements occur when tunnelling is near the pile toe. The second tunnel further increases movement toward the first tunnel due to degraded ground stiffness. Compared to elevated battered pile groups, battered piled rafts exhibit significantly reduced lateral displacements, deflections, and settlements because of additional resistance from raft-soil interaction. Twin tunnelling in each case also alters axial load distribution. Twin tunnelling near pile shaft caused reduction of 61% in shaft resistance whereas 20% of end-bearing decreased in twin tunnelling near pile toe. The maximum bending moments were induced near the pile head in battered elevated pile group but are smaller in piled rafts (up to 30% reduction) in each case.