Estimating slope of critical state line from cone penetration test

Estimating slope of critical state line from cone penetration test — an update

David Reid

Estimation of density from cone penetration test (CPT) results is challenging, as cone resistance is a function of a number of soil properties, particularly compressibility. While many of the relevant soil properties can be determined from laboratory testing of recovered samples, this process is not feasible when investigating a deposit of soil with significant variations in gradation and (or) properties across depth and lateral extent. To provide a first-order estimate of density from CPT results alone, a number of correlations have been developed to ascertain other soil properties, particularly compressibility, from CPT data. In particular, friction ratio and soil behaviour type index have been suggested as providing indications of soil compressibility, referenced as the slope of the critical state line. Two of these correlations are critically assessed through the identification and analysis of data from 31 sites where both CPT and relevant laboratory testing were conducted. This process indicates that while the additional data analyzed in this study are generally consistent with previous correlations in terms of trend, significant scatter is evident. In addition, the difficulty in directly relating recovered samples to specific CPT data is outlined.