Evaluation of Direct CPT Methods for Estimating the Ultimate Capacity of Driven Piles

The cone and piezocone penetration tests (CPT and CPTu) have been widely acknowledged as a useful in situ tests for subsurface investigation and soil characterization. The CPT is fast, robust, and economical test that can provide continuous soundings with depth. Due to similarity between pile and cone, the estimation of pile capacity from CPT data was among the earliest applications of the CPT. Accordingly, different direct Pile-CPT methods have been developed based on this analogy between the cone and the pile. Analyses and evaluation were conducted on eighty driven friction piles of different sizes and lengths that were failed during pile load tests. The Pile-CPT methods were used to estimate the load carrying capacities of the investigated piles (Q(p)). The Davisson method was used to determine the measured load carrying capacities from pile load tests (Q(m)). Four criteria were selected to evaluate the performance of the different Pile-CPT methods: the best fit line for Q(p) versus Q(m), the arithmetic mean and standard deviation for the ratio Q(p)/Q(m), the cumulative probability for Q(p)/Q(m), and the histogram and log normal distribution for Q(p)/Q(m). Results of the analyses have been used to evaluate the ability of different Pile-CPT methods for estimating the pile capacity. The results of this evaluation, the probabilistic, UF, and Philipponnat methods showed the best performance methods, followed by De Ruiter and LCPC methods, which were ranked next. The UWA and CPT2000 methods showed acceptable performance, too.