Analysis of CPTu data from the North Sea region to estimate the frequency of inaccurate pore pressure measurements

Cone Penetration Testing with pore-pressure measurements (CPTu) is the main site characterization test because of its ability to provide stratigraphy, as well as mechanical and hydraulic properties. Malfunctioning of the piezocone equipment, as well as poor calibration and/or maintenance, can lead to poor data quality, and therefore, there are clear procedures in place to avoid such instances, which can be considered quite rare. However, saturation of the piezocone pore-pressure measuring system, which is a key to reliable results, is a significantly more common source of erroneous measurements. The great variety of saturation methods and media encountered in engineering practice is symptomatic of the empirical approaches applied to solve this type of uncertainty. We performed a systematic analysis of open-source data available from the UK, Germany, the Netherlands, and Belgium and analyzed the data to identify measurement repeatability and calculate the frequency of occurrence of inaccurate measurements in the pore pressure response based on site conditions. The analysis of pore-pressure measurements in clean sands, which was primarily based on the IJmuiden Ver wind farm in the Netherlands, showed that approximately 34% of the tests that appeared to follow a hydrostatic profile may nonetheless diverge significantly.