Evaluating ε50 for lateral load-displacement behavior of piles in clay

Analyzing piles subjected to lateral loads significantly depends on soil resistance at any point along the pile as a function of pile deflection, known as P-Y curve. Besides, this curve is considerably affected by deformation characteristics of soil defined as “the soil strain at 50% of maximum deviatoric stress (ε50)”. In this research, several models are proposed based on the strength and deformation characteristics of soil. These models are applied to predict ε50 and specifically to investigate the lateral behavior of very long pile foundations of offshore oil and gas platforms in South Pars field in Persian Gulf, Iran. Herein, evolutionary polynomial regression (EPR) is used to obtain ε50 from extensive soil data of marine clays including in-situ and laboratory test results. It is shown that more realistic values of ε50 are obtained from cone tip resistance of CPT comparing to that of laboratory-derived undrained shear strength parameter. The results obtained from the most appropriate proposed model (Model 5) are compared with those of existing ones, available in the literature. The application of this model is investigated in predicting lateral load-displacement of tested full-scale piles. It is shown that the results predicted by Model 5 agree relatively well with the measured values. Furthermore, Model 5 has been successfully verified by the data obtained from another surveyed area, outside the main studied area used for its development.