Effect of OCR and Pile Diameter on Load Movement Response of Piles Embedded in Clay over Time

Abstract

The main causes of soil setup effects on pile response are generation of excess pore water pressure (EPWP) due to installation of prefabricated piles in saturated soils and subsequent dissipation of EPWP and, hence, stress state variations around the pile shaft. The main objective of this paper is evaluating the effects of pile diameter and over-consolidation ratio (OCR) on variations of stress state in soil adjacent to the pile and variations of the pile ultimate load over time using a nonlinear finite-element method numerical scheme and comparisons with field test data. The numerical model involves simulation of the pile penetration throughout the installation process and, hence, simulation of EPWP inducement and its dissipation over time during consolidation. The field data include pile driving and load test data in normally consolidated (soft) and overconsolidated (stiff to very stiff) fine-grained strata. The results have shown that the ratio of EPWP dissipation to overconsolidation stress reduces with an increase of OCR. The coefficient of lateral soil pressure has also increased with OCR and pile diameter. A “setup ratio” is defined as the ratio of shaft resistance at the end-of-consolidation to end-of-drive and is shown to have a proportional relationship with the pile diameter and a nonlinear and reducing trend with an increase in OCR. Correlations are proposed to modify existing relations for an increase in shaft resistance with time, incorporating OCR and pile diameter as well. Finally, the field data interpretations of a site having sufficient pile-load testing data in normally and overconsolidated fine-grained stratifications have validated the findings of the numerical model.