Shaft Capacity of Displacement Piles in Clay Using the Cone Penetration Test

The prediction of the shaft capacity of displacement piles in clay still relies wholly on empirical or semiempirical approaches. This paper examines the predictive abilities of five well-known methods against an extended version of an existing database of pile tests. It is seen that coefficients of variation (COVs) of the ratio of calculated to measured capacities (Q(c)/Q(m)) are significantly higher than expected. The paper then uses the database of shaft capacities to examine potential relationships between local shaft friction and the cone penetration test end resistance (q(t)). Predictions are subsequently compared with capacities measured in a series of centrifuge tests and with the distributions of peak frictions observed in two well-documented field tests. Widely different formulations adopted by each of the existing empirical methods give broadly similar COV values for Q(c)/Q(m) ratios, and it is concluded that the database of high-quality pile tests needs to be expanded significantly if the reliability of estimates of shaft capacity in clay is to be improved. DOI: 10.1061/(ASCE)GT.1943-5606.0000749. (C) 2013 American Society of Civil Engineers.