Behavior of Rigid Piled-Raft Foundation Subjected to Compressive Loading Considering Time Effect: An Experimental and Analytical Study

Field load tests are carried out on a single pile and piled-raft foundation (PRF) consisting of a 2 x 2 pile group with consideration of the time effect. The piles along with the raft in the PRF have been instrumented with load cells and strain gauges. Gradual compressive loading has been applied to the PRF with an increment of 10% up to the estimated safe load capacity. Settlement corresponding to the safe load is monitored for 4 months. The settlement of the PRF, axial load carried by piles, shaft friction along the pile length, moments in the raft, and load sharing ratio between piles and raft for each increment of loading are observed with respect to time. A nonlinear analysis is suggested to scrutinize the behavior of vertically loaded rigid PRFs in layered soil medium (present approach). Considering the theory of the interaction factor, an approximate procedure is implemented to analyze the nonlinearity of pile groups with a rigid raft. Additionally, the nonlinear response of piles using hyperbolic functions is presented (alternative hyperbolic function approach). A simplified method for the calculation of the flexibility matrix considering the time effect is also suggested (present time-based approach). The analyses are validated with the field results and available literature. Parametric studies have been performed to calculate the immediate and time-dependent settlements of the PRF by varying the length to diameter ratio of the pile, spacing to diameter ratio of the pile, and pile group configuration using the present approach and present time-based approach. Immediate settlements corresponding to the safe load by the present approach and alternative hyperbolic function approach are approximately 8.18% and 6.48% less than the measured settlement.