Anisotropy effects on the undrained stability of cuts in clays

Abstract

It has long been recognised that soils are generally anisotropic with some of their properties varying depending on the direction of measurement. In particular, strength anisotropy should be a main concern in relation with the stability assessment of geotechnical cases. Nevertheless, the incorporation of this feature is rarely considered in routine slope stability analyses in spite of the fact that its absence may lead, in some cases, to an overestimation of the factor of safety. In the paper, the effects of strength anisotropy on the undrained stability of cuts in clays are examined. A literature review reveals that clays have different patterns of undrained strength anisotropy depending on their overconsolidation ratio. A constitutive model is introduced, able to account for the different observed variations of undrained strength with loading direction. A series of numerical stability analyses have been performed to explore the effects of the type of undrained strength anisotropy on the stability of cuts. The effects of slope inclination, bedding orientation, and pattern of undrained strength anisotropy on factors of safety and failure mechanisms are examined and discussed. In addition, a real case study of the failure of an underwater cut is analysed showing that undrained strength anisotropy is able to explain satisfactorily the collapse observed.