Material-specific interpretation of the state parameter from drained cone penetration test

The Cone Penetration Test (CPT) is a widely used site investigation tool due to its accuracy and wealth of data at a relatively low cost. Virtually all CPT interpretations explicitly or implicitly depend on how the in-situ state parameter is correlated to the tip resistance. Accurate interpretation of the state parameter from CPT is the basis for evaluating strength and liquefaction susceptibility of granular soils. The handful of interpretation methods used in the industry range between empirical and semi-empirical. As is the case for all empirical methods, extrapolating these methods outside of the original database, especially to significantly different soils such as silt-rich tailings, brings about significant risk. This paper presents a new method of interpreting the state parameter from a fully validated model of the cone penetration in sand. The method has no empirical elements and produces soil-specific correlations between the tip resistance and the state parameter. It can be easily implemented in a spreadsheet and does not require complicated analyses. The method differentiates among soils through calibration of a critical state based constitutive model, Norsand, through triaxial compression tests. The potential errors induced by not measuring soil properties are quantified.