Comparative performance of 5 cm² and 10 cm² piezocones in a lacustrine clay

A piezocone investigation has been carried out in a deep deposit of glacial lacustrine clay using piezocones with cross-sectional areas of 5 cm 2 and 10 cm 2 . The piezocone tests formed part of a larger soil characterisation study, but this paper focuses on the relative performance of the piezocones in profiling the clay. It is shown that using a 5 cm 2 piezocone rather than a 10 cm 2 one significantly improved the detection of relatively thin silt layers within the lacustrine, and occasionally varved, clay. The feasibility of detecting silt layers as thin as 2–4 mm and of matching the piezocone responses associated with silt layers at different test locations, thereby allowing an assessment of their continuity, is demonstrated. There were no significant differences between the magnitudes of the cone resistance and excess pore pressure recorded in the clay with 5 cm 2 and 10 cm 2 piezocones. Pore pressure dissipation test results were variable but, in a region where no silt layers were detected, similar results were obtained with piezocones of each size.