LRFD for pile foundations

Load and resistance factor design (LRFD) has come into wide use for foundations. However, present-generation resistance factors in LRFD calibrated with traditional factors of safety do not reflect to any effects of significant degree the variance and bias in external load effects and limit state resistance. The purpose of this paper is to determine rational resistance factors for driven piles in overconsolidated clay at the University of Houston National Geotechnical Experimentation Site (NGES-UH). The nine group pile and two single piles tested to failure axially were used to estimate ultimate pile resistances using three CPT-based methods and two alpha -based methods. The 26 CPT sounding data performed in close proximity to the piles were characterized by geostatistical method in order to estimate spatial variability effects of soil properties on ultimate pile resistance computation, The rational resistance factors developed for the piles using an LRFD model coupled with the first order second moment reliability model are between 0,55 and 0.60 for three CPT-based methods, and 0.30 and 0.50 for Tomlinson a-based method and API alpha method, respectively, for levels of target reliability index beta (T) = 3,5.