Centrifuge and numerical modelling study on the response of piled raft foundations to tunnelling

Tunnelling adjacent to or beneath piled foundations is a common yet challenging scenario in urban underground construction. In this study, the settlements and load transfer behaviours of piled raft foundations under tunnelling were investigated. Five 60g centrifuge model tests were performed, and 28 three-dimensional numerical simulations were used to examine the influences of the foundation location, raft dimension, raft embedment depth and foundation–soil interface friction coefficient on the tunnelling-induced response of foundations. The results show that tunnelling induces progressive foundation settlement and redistribution of the load within foundation systems. Compared with single piles, piled raft foundations have smaller settlements. For foundations located directly above the tunnel, tunnelling transfers load from the pile base to the pile shaft and raft, whereas this transfer direction changes as the offset distance increases. Compared with the raft embedment depth, the raft dimension has a greater influence on reducing settlement and increasing the contribution of the raft load. A higher interface friction coefficient increases shaft friction mobilisation, but its effect on piled raft settlement is limited. These findings improve the understanding of tunnelling-induced foundation response and provide guidance for the design and assessment of pile-supported structures in urban underground engineering.