Using SHANSEP for verification of unreliable piezocone data in clays

The evaluation of the undrained stability of old embankments on soft clays relies upon the accurate modelling of undrained shear strength in the subsoil. It is vital to account for the effects of consolidation to determine the increased shear strength below the embankment. The CPTU test is a fast in-situ test that provides continuous measurements with depth and can be easily performed through the embankment to evaluate the strength increase. The interpretation of undrained shear strength from CPTU requires the selection of cone factors, which are normally based on laboratory or in-situ (e.g. field vane) tests or empirical correlations. However, CPTU measurements can be negatively affected if the test is poorly executed or if the apparatus lacks proper calibration. This paper discusses how the SHANSEP empirical model for clays can be used to verify the reliability of the available CPTU measurements in a given site investigation case. Further, the paper attempts to provide insights into the selection of empirical cone factors for modelling undrained shear strength for embankment stability. The SHANSEP model describes the undrained shear strength of clays in terms of normalized properties, where the soil strength is defined by means of the overconsolidation ratio (OCR) and two material coefficients that require empirical calibration. The applicability of the method is presented for a case study from Western Finland, where CPTU testing was carried out both on the side and underneath an old railway embankment. The results of the study are exploited to suggest recommendations for engineering practice.