The Role of Full Scale Testing in ASD and LRFD Driven Pile Designs

For design of foundations on driven piles, Load and Resistance Factor Design (LRFD) is increasingly replacing the conventional Allowable Stress Design (ASD) approach. LRFD separates the uncertainty in loading conditions from the uncertainty in resistances, while the ASD approach uses a single "global factor of safety" to cover all uncertainties. Concerning resistances, LRFD uses a range of "resistance factors" adjusted to the method of capacity evaluation and level of quality control and assurance during construction, while the previous ASD approach often considers only the method of capacity evaluation but not the amount of testing. Considerable confusion exists as to how to best apply the new LRFD methodology and reap its potential benefits to affect a safe and economical foundation. This paper attempts to address some of the issues and answer questions associated with the newly implemented method. The benefits of full scale pile testing, by either static or dynamic methods, and of an increased amount of such testing, are illustrated by numerical examples. After a review of the global factors of safety for different codes, pile designs using ASD global factors of safety are compared with designs produced using the most recently developed LRFD resistance factors from AASHTO Specifications. Among the capacity evaluation methods will be static analysis, dynamic formula, wave equation, dynamic testing and static testing. Although the prime emphasis is the AASHTO specification, comparisons are also made with resistance factors from current standards from Europe, Australia, and Canada.