OasisLMS

Piled raft foundations (PRFs) offer distinct advantages over other shallow or deep foundation systems due to the combined load-bearing capacity of both the raft and piles. However, analyzing and designing PRFs is complex due to the intricate three-way interaction (raft-pile-soil) in response to varying loads, structural configurations, and soil properties. This study investigates 20 different types of rectangular piled rafts embedded in four distinct clay types (Boston blue clay, London clay, Shanghai clay, and San Francisco Bay mud) with varying overconsolidation ratios (OCRs 1 to 5) using three-dimensional finite element analysis in Abaqus software. The aim is to comprehend their short and long-term load-settlement behavior.

The critical state-based Modified Cam Clay (MCC) model is employed to capture the elasto-plastic behavior of consolidating clay under single-drainage conditions with upward flow. Settlement of piled rafts comprises immediate and consolidation settlement. Immediate settlement occurs during the application of external loads, caused by nonlinear elastic deformations in the soil, regardless of load duration. Consolidation settlement, on the other hand, arises from elastoplastic soil deformation coupled with excess pore pressure dissipation. Immediate settlement can be significant, especially in overconsolidated clay deposits, necessitating consideration alongside consolidation settlement in total settlement assessments. The degree of consolidation versus time response of piled rafts is largely independent of raft geometry but influenced by OCR during initial stages, albeit marginally above 55% consolidation. Moreover, the maximum piled raft settlement is anticipated to exceed average total settlement estimations by approximately 24%, with differential settlement in piled rafts constituting around 6% of the average total settlement.

In summary, this study sheds light on the intricate behavior of PRFs in various clay types and provides insights into settlement mechanisms critical for effective foundation design and performance evaluation.

Priyanka Bhartiya, Cowi India Ltd.; Tanusree Chakraborty, IIT | Delhi; Dimpanjan Basu, University of Waterloo

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