Improved determination of the constrained modulus in soft soils using the flat dilatometer test

A wide range of geotechnical tasks demand a reliable determination of soil stiffness. Since undisturbed soil sampling is required but difficult for laboratory testing, parameter identification based on in-situ testing in combination with correlations have become more popular. Flat dilatometer testing (DMT) considers the penetration of a steel blade, equipped with a circular, expandable membrane, into the ground. The penetration process is usually stopped in 20 cm intervals for total stress measurements at defined membrane expansions. The present article aims to improve the determination of the in-situ constrained modulus in soft soils by means of DMT. Existing correlations are compared with oedometer results for Alpine deposits. It is shown that constrained moduli, derived from existing correlations, underestimate laboratory results, even when DMT readings are corrected for partial drainage effects. New correlations are developed to reach a better agreement between in-situ and laboratory results in fine-grained soils.