Use of Norwegian National Test Sites to evaluate CPTU correlations embedded in software

Commercial software packages that utilise published CPTU correlations are frequently used for quick presentation of soil parameters such as soil unit weight, over consolidation ratio, undrained shear strength, lateral stress ratio, and peak friction angle. It is a well-known fact that such correlations are not globally valid, but many practitioners use the parameters obtained this way even in foundation design. At the Norwegian soft clay, quick clay, silt, and sand sites, high quality sampling and laboratory testing have resulted in a consistent representative database of reliable soil parameters. Moreover, high quality results of CPTU, seismic cones, self-boring pressuremeter and a novel flow cone tool are also available at the sites. Using these high-quality benchmark parameters gives an excellent opportunity to evaluate the validity of the soil parameters derived from 18 published CPTU correlations used in commercial software packages. For transparency, the correlations are described in some detail with full reference to the source. A comparison of correlation derived parameters and reliable laboratory-based benchmark soil parameters showed that the use of global correlations can be too conservative and, in some cases, dangerous. Local correlations are not only recommended but are essential for design. In this study, we did not cover highly overconsolidated clays and very dense sands, though similar conclusions on those soils may be expected.