Slope stability in natural slopes with vertical or principal stress induced undrained shear strength anisotropy

Abstract

In this master thesis an implementation of a user defined soil model in PLAXIS is presented. The new soil model has been coined ADPXX; the shear strength anisotropy in the ADPXX model may be defined to the direction of the principal stress, rather than the standard horizontal-vertical undrained shear strength anisotropy. The reasoning behind the modification of the anisotropy is the assumption and belief that a soil accommodates its strength to the stress situation it is consolidated under.

The author did not find any literature specifically on the shear strength anisotropy of clay in slopes. In Andersen (2009) some DSS test on a marine clay with different consolidated shear stresses are discussed. There was a clear indication that the undrained shear strength was increased with the relative consolidated shear stress. On the basis of that assumption, and a project thesis on the same topic that yielded preliminary resultspointing to the direction of the shear stress being an important factor in slope stability, the soil model ADPXX was created in order to investigate the subject by simulation in PLAXIS.

The results from the testing of the soil model in PLAXIS reveals a significant difference in slope stability between strict horizontal vertical anisotropy and the anisotropy inclined towards the principal stress.