Comparing CPT and pile base resistance in sand

White, David J. and Bolton, Malcolm D. (2005) Comparing CPT and pile base resistance in sand. Proceedings of the Institution of Civil Engineers: Geotechnical Engineering, 158 (1), 3-14. (doi:10.1680/geng.158.1.3.56645).

Record type: Article

Abstract

The comprehensive database of load tests on closed-ended piles in sand has been re-examined to study the relationship between CPT resistance, q_c, and ultimate base capacity, q_b. The aim is to establish the origin of low reported values of q_b/q _c which contrast with continuum models that suggest q _b = q_c for steady deep penetration. Partial embedment of the pile tip into a hard layer underlying weak material has been accounted for by weighting q_c. Partial mobilisation has been accounted for by defining failure according to a plunging criterion. When these two mechanisms are considered, the resulting values of q_b/q_c have a mean value of 0·90 and show no trend with pile diameter. The remaining slight underprediction of the 'continuum' model (q_b = q_c) could be attributed to the underestimation of plunging load in pile tests for which steady penetration is not reached. This exercise makes two contributions: first, it is suggested that any reduction of q _c when estimating the end bearing capacity of closed-ended piles in sand should be linked to partial embedment and partial mobilisation, rather than absolute diameter; second, the dearth of high-quality pile load test data in the public domain is highlighted.