Load-Settlement Response of Cushioned Piled Rafts with Varying Pile Lengths to Retaining Wall Movement

Failure of an excavation support structure will inevitably result in stress state changes and ground settlements behind the wall, affecting the serviceability of adjacent structures. Such excavation-induced effects on existing piled rafts received little attention in the literature. This paper aims to investigate the load-settlement behaviour of existing disconnected piled rafts (DPR) with unequal pile lengths that were arranged beneath the cushion in various practical configurations. The DPRs were subjected to a passive loading triggered by an adjacent rigid retaining wall movement. ABAQUS was utilized to carry out the three-dimensional finite element analyses. The numerical approach was validated by experimental studies on DPRs with 2 x 2 long and short rigid piles close to a rotating retaining wall. The results show that the arrangement of the group's long and short piles has a significant impact on the overall settlement and tilting of the raft. An increased number of long piles close to the wall helps to recede the additional foundation settlement caused by the wall movement. The stiffness of the foundation soil effects the load-settlement response as well. The stiffer the subsoil, the greater the proportion of the applied working load carried by the soil prior to wall movement and the larger the amount released as the wall movement progresses. The vertical loading history prior to wall movement significantly affects the foundation settlement behaviour, with wall movement causing the 3 x 3 piled raft's settlement to increase by up to 21.7% for a working load increase from 180 to 900 kPa.