The Axial Capacity of Closed-Ended Pipe Piles Driven in Gravelly Sands

In situ test-based pile design methods are often used to estimate the ultimate capacity of closed-ended pipe piles (CEPs). Among these, methods based on the cone penetration test (CPT) prove to be the most accurate. However, in soil profiles with high gravel contents (e.g., >20%), these CPT-based methods tend to overestimate pile capacity. In this paper, we present the results of an instrumented static load test (SLT) performed on a 17.7 m (58 ft) long CEP with an outer diameter of 610 mm (24 in.) driven in a soil profile with gravelly sand layers. We compare the shaft and base resistance components measured from the SLT with estimates from three widely used CPT-based pile design methods. We also review additional cases of high-quality SLTs performed in gravelly soil profiles to provide context for the observations from the current SLT. Depending on the gravel content of the layers in the soil profile, predictions from CPT-based design methods tend to overestimate the ultimate pile capacity by a factor ranging from 1.2 to 2.6.