NCDOT’s Experience in Load and Resistance Factor Design and Construction of Driven Pile Foundations

摘要

NCDOT’s LRFD practice of driven pile foundations for highway bridges is presented and theissues encountered in both design and construction stages of the LRFD projects are discussed.Also, case studies of three projects are presented. The NCDOT LRFD policy generallyfollows the procedures and requirements of the AASHTO LRFD Bridge DesignSpecifications with some exceptions in the use of the resistance factors. The LRFD practiceresults in somewhat more conservatively designed and costly bridge foundations due to thefact that NCDOT used a safety factor of two as the minimum safety factor to compute bothnominal static bearing capacity and required driving resistance in the ASD practice and theresistance factors used in the LRFD practice are equivalent to safety factors larger than two.Exceptions to the policy were allowed in the design of a few projects to avoid overlyconservative design compared to the ASD practice. The AASHTO’s requirement of dynamictests with signal matching analysis of at least one production pile per pier to use the RF of 0.6seems to be irrational and impractical, and it should be reevaluated and revised. Thetransition of the NCDOT’s bridge foundation design from ASD to LRFD has been donesuccessfully with a minimal disruption to the projects’ schedule. NCDOT plans to recalibratethe resistance factors when sufficient design, construction, and load test data becomeavailable.