ABSTRACT
Currently the p-y method is widely used in industry to model the pile behavior under lateral loads. Appropriate p-multipliers and y-multipliers are usually applied to the “backbone” p-y curves in order to account for group effect or any other possible influence on the pile lateral behavior. At Piers 76 and 77 of Pulaski Skyway, deep foundations with groups of drilled shafts are proposed to replace the existing caisson foundations. The existing caisson foundations will be left in place and hence may influence the drilled shaft behavior. In this study, a numerical model was developed to investigate the possible effect on drilled shaft lateral behavior due to the existing caisson. A 2D analysis was performed using the commercial finite difference program FLAC. A plain strain condition was assumed in a homogenous soil layer and the shaft was subjected to a lateral force directed towards the caisson. The lateral response behavior was evaluated in both soft clay and medium stiff clay. The effect of interface roughness (rough or smooth) between shaft-soil and caisson-soil were also investigated. First, the lateral behavior of drilled shaft was calibrated with the “backbone” p-y curves. Next, the p-y curves were compared between “with caisson” and “without caisson” conditions. It is found that the soils exhibit a slightly stiffer behavior at small shaft deflections with the caisson presence, particularly for a rough soil-structure interface. However, the soil ultimate resistance may be lower with the caisson than without the caisson, particularly for a smooth soil-structure interface. It is also observed that the displacement level to fully mobilize the soil resistance with the caisson is significantly less than that required to fully mobilize the resistance without the caisson. For a full-range p-y curve, therefore it may be necessary to apply both p and y multipliers. Nevertheless, under service conditions that the shaft deflection is small (e.g. less than 2.5 cm), such effect is minor and the “backbone” p-y curves may still be applicable with the caisson presence.
