A Simplified Settlement Prediction Method for Piled Rafts in Clay

A method for estimation of nonlinear, time-dependent settlement of piled raft foundations (PRFs) embedded in saturated clayey soils subjected to uniformly distributed load under the single drainage condition is developed. Twenty different rectangular PRFs resting on four different types of normally consolidated to moderately overconsolidated clays (Overconsolidation ratio, OCR = 1, 2, and 5) are analyzed to quantify their short- and long-term settlements. Rigorous three-dimensional, elasto-plastic finite element (FE) analyses are performed with the critical state-based Modified Cam Clay (MCC) soil constitutive model. The coupled consolidation theory of Biot is used to model the time-dependent dissipation of excess pore pressure under the single drainage condition. The FE analysis results are used to systematically investigate the influence of time and various soil and PRF parameters on the settlement response of piled rafts. Based on the study, fitted equations are developed correlating PRF settlements and degree of consolidation with various influencing parameters. The proposed equations can predict with reasonable accuracy the immediate and primary consolidation settlement as well as the degree of consolidation, and can be used at the initial design stages.