CPT-based design of pile foundations in sand and clay: Perspectives

Abstract

This paper provides some perspectives and guidance for the design of pile foundations in sand and clay using cone penetration test (CPT) results. A key variable in the estimation of the limit unit shaft resistance qsL of piles in sand is the critical-state interface friction angle δc, which is a function of the critical-state friction angle ϕc of the sand. In the absence of direct shear or triaxial compression test results, which is often the case for routine infrastructure projects, engineers typically assume a conservative value for ϕc in pile design. In addition, effective stress-based methods for estimation of qsL of driven piles in clay rely on the residual interface friction angle δr, among other variables; however, in these methods, δr does not vary with the normal effective stress on the pile operative at the time of shearing. In this paper, we present relationships and approaches to address these issues. Finally, a relationship between the cone resistance qc and the corrected standard penetration test (SPT) blow count N60 was also developed so that engineers may obtain an estimate of qc for use in a CPT-based design method when only SPT blow counts are available for a site.