On the Benefits of Incorporating Anisotropy in Stability Analyses in Sensitive Clays

During construction of E45 – Norge/Vanerbanan, analyses of an area located in Agnesberg, just north of Gothenburg, showed an evaluated factor of safety significantly less than prescribed in the codes for both the new main road E45 and the new railway Norge/Vanerbanan. The road and railway are situated very close to each other, just next to the Gota River that complicates the evaluation of the safety factor. The empiricism commonly used was questioned due to an unfamiliar change in undrained shear strength in the profile. Consequently, an extensive field and laboratory campaign was conducted to establish a more accurate and reliable strength profile. The extensive laboratory programme contained a number of direct simple shear tests, as well as triaxial tests in both compression and extension to be able to determine the strength anisotropy in the area. The laboratory study showed that the soft clay in the area was more anisotropic than anticipated, which was more favourable in the studied case regarding the stability. This lead to a new anisotropic function to be used in evaluation of the safety factor. This combined with a general increase in undrained shear strength for the entire profile highlights the potential cost savings resulting from extensive site investigation that incorporates evaluation the magnitude of strength anisotropy.