Comparison between in situ cone resistance and laboratory strength for overconsolidated north sea clays

Abstract Cone resistance and laboratory strength measurements have been compared for stiff overconsolidated clays from five oil and gas fields in the North Sea. The clays considered are glacial in origin. The best agreement between cone resistance and laboratory strength is found by using an Nk factor equal to 17 in the formula qc = Nk . Su + γZ. The study shows that the cone gives highly reproducible results, whereas there is a considerable scatter in the laboratory strength determinations. When making use of CPTs for preliminary design, the authors recommend assuming an Nk of 15–20, depending on the type of problem under consideration.