Assessment of Undrained Soil Strength Using the Fall Cone Test and Empirical Modelling

Abstract

Typical empirical correlations in geotechnical practice can be useful for estimating the values of necessary parameters to be used in design and geotechnical calculations. For fine-grained soils, undrained shear strength is a key parameter recommended by Eurocode 7 and is strongly influenced by water content. This paper investigates the relationship between water content, fall cone penetration, and undrained shear strength of medium-plasticity silty clays based on an extensive laboratory dataset obtained over a wide range of moisture conditions, including values both below and above natural water content. The analysis is conducted on remoulded soil samples. Power-law relationships between water content and cone penetration were established, and the corresponding parameters were evaluated and compared with values reported in the literature. The undrained shear strength-water content relationship was further analyzed using normalized expressions based on the water content ratio, enabling direct comparison with existing empirical models. A within-sample regression approach was applied to account for repeated measurements on individual soil samples, revealing consistently high coefficients of determination and a narrow range of regression slopes across materials. The results demonstrate that systematic laboratory testing combined with appropriate data normalization and within-sample analysis provides physically meaningful and robust empirical relationships. A site-specific empirical model for estimating undrained shear strength is proposed, offering improved reliability compared to generalized correlations and supporting more accurate site-specific geotechnical assessments.