On the use of embedded pile elements for the numerical analysis of disconnected piled rafts

Abstract

Piled rafts (PRs) are widely employed to provide the foundations of high-rise buildings with both large bearing capacity and satisfactory settlement performances. In recent years, at variance with standard engineering practice, piles have been not infrequently designed with no structural connection to the raft, in order to let them mostly work as settlement-reducers. The analysis and design of disconnected piled rafts (DPRs) are made challenging by the occurrence of complex soil–structure interactions, including the load transfer mechanism through the raft–pile gap. While non-linear finite element (FE) simulations can improve the design reliability, excessive computational costs are likely to arise in the presence of large pile groups. To mitigate this shortcoming, PR/DPR FE models are often endowed with so-called “embedded piles” (EPs), i.e. 1D beam elements embedded into discretized soil domains.This paper tackles relevant issues related to the practical use of EPs for large DPRs, i.e. to setting up/calibrating FE elasto-plastic models combining bearable computational time and reasonable accuracy. Special attention is devoted to modelling the aforementioned stress transfer through the raft–pile gap, as well as the soil–pile connections (interface elements). Finally, the reliability of EP predictions is verified against the numerical results from previous “fully solid” (FS) DPR analyses (with no use of EPs).