Integral pile shaft-columns have been increasingly used for bridge foundations in California because of the economical construction of large diameter Cast-In-Drilled-Hole (CIDH) piles. The current design method of piles against lateral loading involves the use of Winkler’s spring concept with the standard nonlinear p-y curves. However, the accuracy of using these p-y curves for large pile diameters is questionable because they were developed based on relatively small pile diameters. This research study focused on an evaluation of the pile diameter effect on p-y curves through analytical and experimental programs. Furthermore, an assessment of inelastic performance of CIDH piles under cyclic loading was conducted.