Influence of soil pile interaction on seismic behavior in sandy condition

Abstract

Damages of structures supported by deep foundations due to complete or partial collapse have demonstrated paramount importance of the understanding of Soil-Pile Interaction (SPI). Kinematic interaction is due to the presence of pile foundation in the ground. Several methods are available to determine the kinematic interaction. Among these approaches, the method of Beam on Nonlinear Winkler Foundation (BNWF) is widely used in research practices. In the BNWF method, soil and pile are modeled as nonlinear springs and linear finite elements, respectively. Stiffness coefficient of spring is evaluated based on load-transfer approach, often known as p-y curve method. On the other hand, the pile group and the single pile behavior are usually different owing to the impacts of the pile-to-pile interaction known as shadowing effects. Shadowing effects are the condition where there is an overlapping of the stress zones. The p-y curve of single pile can be used in pile group based on p-multiplier concept. Many investigators have developed p-y curves for sandy and clayey soils. However, these developed curves do not account some parameters such as relative density of sandy soil and side friction. This research has developed a new p-y curve for single pile under lateral loading through a comprehensive experimental investigation on Johor Bahru Sand. A good estimation of soil properties in the laboratory was required to simulate natural soil condition. In this study, sand samples prepared using new Mobile Pluviator designed to achieve of the desired relative densities ranging from 10% to 98%. A series of 12 different configurations of piles groups investigated in loose and dense sandy conditions to evaluate the piles interaction effects. The p-y multiplier factor was determined for the piles in the group based on distribution of load applied among the pile groups. The results of different configurations of pile group showed that the ultimate lateral load increased by 53% in increasing of spacing center-to-center piles (s) from 3D to 6D (D=pile diameter) owing to the reduction of pile group interaction effects that improve the performance of the pile group efficiency. A ratio of s/D more than 6 was large enough to eliminate the effects of pile group interaction. The new p-y curve exhibits a lower initial stiffness compared to the p-y curves from previous researchers. The maximum values of displacement and seismic acceleration of the structure occurred almost at the same time for existing and new p-y curves, but the new p-y curve can determine the seismic behavior under the strong earthquakes more accurate than the existing curves because of the higher ultimate lateral resistance.