CPT-Based Design Method for Axial Capacities of Drilled Shafts and Auger Cast-in-Place Piles

The paper presents observations from a newly compiled database of static load tests comprising 68 instrumented drilled shafts and auger cast-in-place piles in sands, sand mixtures, silt mixtures, and clays at 37 sites around the world. The measured unit shaft friction and base resistance of the database piles are compared with values calculated using well known methods that correlate capacity directly to the cone penetration test (CPT) end resistance. It is shown that the updated Laboratoire Central des Ponts et Chaussées (LCPC) method in 2012 is the best performing of existing CPT-based methods. A new CPT approach is proposed that, similar to other recently published approaches and experimental studies, involves the soil behavior type index (Ic) determined in CPTs in the formulation. This approach can be expected to lead to more reliable estimates of pile capacity as it provides an improved fit to the new database while also being consistent with the trends implicit in the LCPC method, which is based on a larger and independent data set.