Early stage design of driven piles primarily relies on static analysis based on one or a combination of total and effective stress approaches, the latter known as the ?-method to estimate axial capacity. A database of 85 piles driven in the Puget Sound Lowland region and monitored at End of Driving (EOD) and Beginning of Restrike (BOR) was compiled along with capacities estimated using the CAPWAP procedure. Established soil profiles based on borings with standard penetration tests (SPT), cone penetration tests, and geologic maps were matched with their corresponding unit shaft resistance profiles from the CAPWAP procedure and resulted in more than 1, 200 observations. In this study, eight new models were developed to predict the ?-coefficients at EOD and BOR, based on the corresponding USCS categorization. Each ?-coefficient model is formulated using a three-parameter exponential function, calibrated to capture the profile of ?-coefficients with depth. These models could benefit the designer by providing them with a simple, empirical model that accounts for soil type and setup in a smooth, continuous function with depth. A parallel analysis was performed to assess the accuracy and variability of the formulated prediction models to facilitate implementation in load and resistance factor design (LRFD).
Subjects: axial bearing capacity, driven piles, end of driving, beginning of restrike, reliability, LRFD
Author: Youssef Bougataya, Geotechnical Engineer, Armin W. Stuedlein, Ph.D., P.E. and Associate Professor
Publisher: DFI