Structural capacity reduction for drilled shafts with minor flaws

The use of drilled shafts has increased in the last decade due to their cost-effectiveness, versatility, and minimal environmental impact compared with other types of deep foundations. The construction process, however, sometimes introduces minor flaws that are not always detectable with well-performed nondestructive evaluation (NDE) processes. The construction method, working environment, and visibility of the end product for a drilled shaft are different from those of an element in the superstructure, yet most structural designers typically attempt to ensure safety in both types of elements using the same resistance factors. This paper summarizes the results from a comprehensive series of research projects involving flawed drilled shafts and investigates the frequency of occurrence of flaws that will not normally be detected by well-executed NDE programs. The results from this study present capacity reduction factors corresponding to worst-case scenarios. These factors should be refined using a probabilistic approach to formulate realistic resistance factors to be used in the structural design of drilled shafts considering the presence of undetectable minor flaws.