Evaluation of Cone Factors For Two Sensitive Clays From The West Coast of Sweden

Abstract

Data from cone penetration tests with pore pressure measurement, CPTu, is com monly used in geotechnical engineering for evaluating undrained shear strength, su, in clay deposits. However, su cannot be obtained directly from CPTu soundings, but is instead estimated using empirical relationships such as the cone factors Nkt and N∆u. The latter relate the normalized penetration resistance or the normalized excess pore pressures from CPTu to the emerging undrained shear strength. These factors may vary with soil conditions, depth, and site-specific characteristics. The aim of this study was to evaluate the relationship between CPTu data and undrained shear strength obtained from triaxial tests, using data from the Kärra and Utby test sites. Furthermore, the study investigated the feasibility of using Nkt and N∆u. The results from this study indicate that the excess pore pressure, ∆u, showed a stronger correlation with the undrained shear strength evaluated from anisotropi cally consolidated triaxial tests sheared in compression (CAUC), than the net cone resistance, qnet. The results also indicate that cone factors should not be treated as constant values for specific soil types, but instead require site-specific calibration. The study highlights the importance of combining CPTu measurements with labo ratory testing and soil classification when interpreting undrained shear strength in clay.