2021 – A generalised CPTu state parameter inversion method based on the NorSand Widget

Kyle Smith, David Reid, Riccardo Fanni

The estimation of in situ state parameter, Ψ, is a critical part of the characterisation of tailings storage
facilities (TSFs) for the purpose of liquefaction screening and stability assessments. The cone penetration test with pore pressure measurement (CPTu) supplemented by laboratory testing form the current state of practice tools to assess in situ Ψ. Recently, cavity expansion-based CPTu inversion methods, in particular the NorSand Widget, have achieved routine adoption for many engineering applications including TSFs. However, application of cavity expansion-based methods is not without limitations; most notably, cavity expansion-based methods rely upon extensive material specific calibrations, therefore, the results of such methods are limited to the specific soil stratum to which they are calibrated. Additionally, partially drained conditions developed during CPTu are not explicitly considered in currently available methods.

In order to overcome these limitations, this paper presents a generalised method to interpret Ψ from either drained or undrained CPTu, based upon material-specific CPTu calibrations obtained from the NorSand Widget. Guidance on interpretation of drainage conditions developed during CPTu is provided to assist in application of the method. As the method is based upon the NorSand Widget, the influence of elastic soil rigidity is explicitly considered; therefore, the method does not suffer from stress level bias common in screening level methods for estimation of Ψ.