Evaluation of the Undrained Shear Strength in Preconsolidated Cohesive Soils Based on the Seismic Dilatometer Test

Abstract

The undrained shear strength in cohesive soils can be evaluated based on measurements obtained from the standard dilatometer test (DMT) using single- and multi-factor empirical relationships. However, the empirical relationships presented in the literature may sometimes show relatively high values of the maximum relative error. The add-on seismic module to the seismic dilatometer test (SDMT) extends parameters measurable in a standard dilatometer test by the shear wave velocity Vs as an independent variable. Therefore, a method for evaluating the undrained shear strength in cohesive soils based on data obtained from the seismic dilatometer test is presented in this study. In the method proposed, the two-factor empirical relationship for evaluating the normalized undrained shear strength τfu/σ’v is used based on independent variables: The normalized difference between the corrected second pressure reading and the corrected first pressure reading (p1 − po)/σ’v and the normalized shear wave velocity Vs/100. The proposed two-factor empirical relationship provides a more reliable evaluation of the undrained shear strength in the tested Pleistocene and Pliocene clays in comparison to the empirical relationships presented in the literature, with a maximum relative error max RE at about ±20% and the mean relative error RE at about 8%.

Theoretical Equations for the Ratio of Undrained Shear Strength to Vertical Effective Stress for Normally Consolidated Saturated Cohesive Soils

“…Several empirical correlations between the undrained shear strength, s u and the preconsolidation pressure,  p ' and between the undrained shear strength,  u and Atterberg limits were obtained. Galas et al (2019) performed triaxial and dilatometer tests on silts and clays in Warsaw, Poland. A correlation equation among the ratio of (s u / v '), the dilatometer pressure, and the seismic velocity measured using seismic dilatometer test was obtained.…”

Interpretation of CPT and SDMT tests for Lublin loess soils exemplified by Cyprysowa research site

“…The movement of ground particles which occurs with shear wave propagation corresponds to very small deformations of the subsoil. The shear wave propagation velocity is the basis for determining the initial shear modulus [20]- [22].…”