Study of Piled Raft Behaviour in Four Distinct Clay Types-Paper

Paper

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The study examines the short- and long-term settlement behavior of 20 piled raft foundation (PRF) configurations in four clays—Boston Blue, London, Shanghai, and San Francisco Bay mud—at overconsolidation ratios (OCRs) of 1, 2, and 5. Three-dimensional finite element analyses in Abaqus used the Modified Cam Clay model and coupled consolidation theory to represent soil behavior and pore-pressure dissipation. The model was validated against centrifuge test results.<br /><br />Settlement develops in three stages: immediate settlement during loading, followed by consolidation settlement that initially follows a power-law trend and later a logarithmic trend. Immediate settlement is significant, particularly in overconsolidated clay, and should be included in total settlement estimates. Settlement decreases as OCR increases, while immediate settlement becomes a larger share of the total.<br /><br />The degree of consolidation is largely unaffected by PRF geometry. OCR influences consolidation in its early stages, but its effect becomes marginal after approximately 55% consolidation. Across the configurations studied, maximum total settlement averaged about 24% more than average settlement, while differential settlement averaged about 6% of the average. Clay type and OCR had limited influence on these ratios compared with foundation configuration.<br /><br />The findings provide preliminary design guidance for PRFs in clays with properties and dimensions similar to those analyzed. Secondary consolidation was not considered.

Keywords

piled raft foundation

settlement behavior

overconsolidation ratio

finite element analysis

Abaqus

Modified Cam Clay

coupled consolidation

clay consolidation

immediate settlement

differential settlement