Assessment of direct cone penetration test methods for predicting the ultimate capacity of friction driven piles

This paper evaluates the applicability of eight direct cone penetration test (CPT) methods to predict the ultimate load capacity of square precast prestressed concrete (PPC) driven friction piles. Analyses and evaluation were conducted on 35 driven friction piles of different sizes and lengths that were failed during pile load testing. The CPT methods, as well as the static alpha and beta methods, were used to estimate the load carrying capacities of the investigated piles (Q(p)). The Butler-Hoy method was used to determine the measured load carrying capacities from pile load tests (Q(m)) The pile capacities determined using the different methods were compared with the measured pile capacities obtained from the pile load tests. Four criteria were selected as bases of evaluation: the best fit line for Q(p) versus Q 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 showed that the best performing CPT methods are the LCPC method by Bustamante and Gianeselli as well as the De Ruiter and Beringen method. These methods were ranked number one according to the mentioned criteria.