Characterization of in-situ effective stress profiles in clays based on piezo-cone penetration test (CPTU) results

The effective stress is an important state soil variable that controls the mechanical behavior of soils. The depth profile of in-situ effective stress is usually determined using soil unit weights obtained from undisturbed soil samples collected at different depths. The undisturbed soil sampling is subjected to various uncertainties, which becomes more pronounced as target depth increases or offshore condition is involved. The piezo-cone penetration test (CPTU) has been widely used for characterizing in-situ soil conditions. While a variety of CPTU-based methods have been proposed for various geotechnical purposes, less attention has been given to the direct assessment of in-situ effective stress. In the present study, a CPTU-based methodology for profiling in-situ stresses in clayey soils is presented.Acorrelation model between the effective stress and the cone penetration resistances is introduced assuming that there is a unique correlation between the cone resistance, effective stress and undrained shear strength. Field considerations for profiling in-situ stresses from CPTU results are presented. Case examples are selected from the literature and adopted to check the validity of the CPTU-based method.