Proceedings of the
9th International Symposium for Geotechnical Safety and Risk (ISGSR)
25 – 28 August 2025, Oslo, Norway
Editors: Zhongqiang Liu, Jian Dai and Kate Robinson
Statistical Analysis and Interpretation of the Uncertainty Inherent to the Effective Friction Angle of Non-Cohesive Soils Determined from Shear Tests
1Institute of Geotechnics, TU Bergakademie Freiberg, Germany.
2Institute of Stochastics, TU Bergakademie Freiberg, Germany.
3Helmholtz-Centre for Environmental Research (UFZ), Germany
ABSTRACT
The effective shear strength is crucial for assessing the load-bearing capacity and serviceability of geotechnical structures. For a fully probabilistic assessment or to determine representative values to be used in the ultimate and serviceability limit state verifications according to EN 1997-1:2024, mean and variability of the shear strength parameters must be quantified. However, unlike other ground properties, the peculiarity of shear strength parameters lies in the fact that they are not directly measured in the laboratory. Instead, they are derived from the relationship between shear stress and normal stress, or effective mean stress, respectively. The interpretation of the results from shear tests is a particular case of a linear regression where the regression parameters are attributed a physical meaning. This makes the uncertainty analysis of tan ϕ' nontrivial. Existing methods often fail to account for different sources of uncertainty. This study focuses on cohesionless soils, discussing a method to estimate the different contributors to the total uncertainty in tan ϕ' using direct shear and triaxial test data from a preliminary ground investigation for an offshore wind farm in Northern Germany. The method is subsequently evaluated using varying sample sizes.
Keywords: Uncertainty quantification, Inherent variability, Measurement uncertainty, Limited number of samples.
