Elasto-Plastic Analysis for Load-Settlement Prediction of Vertically Loaded Cushioned Piled-Rafts with Unequal Pile Lengths

High-rise buildings built on cushioned piled raft foundations with long and short piles are constantly appearing as a result of the faster process of urbanization and the increasing scarcity of land resources. Accordingly, it is crucial and timely to investigate their load-carrying behavior. Introducing a cushion layer between the raft and piles provides pressing analytical modeling problems. The use of unequal pile lengths further complicates the modeling of several interactions among the group. This article proposes a framework that would estimate the load-settlement response by taking into account the interactive effects among the foundation elements. The relative soil-pile displacement and its relationship with the side frictional resistance of the piles (and/or pile-toe resistance) are used to define the elasto-plastic pile-soil interface behavior, considering the mobilized negative skin friction. The cushion is represented by Winkler's spring approach. The prediction from the proposed method is compared with the load-settlement results from a relatively large-scale indoor experiment and static load test conducted on a 2x2 m disconnected piled raft that has two long and two short piles, which demonstrates good agreement between them. The method suggested in this paper may be useful in understanding how the pile-soil system of a cushioned piled raft with non-uniform pile lengths progressively fails under various loading conditions.