ABSTRACT
This paper investigates delayed slope failures in stiff structured clays under dry conditions, via 2D finite element analyses. The soil is described by a new rate-dependent constitutive model, which includes structure and its degradation by creep strains including post-peak strain softening by creep shear strains. The analyses show that in a slow creeping slope, the stress states are initially below the failure envelope and thus the slope is stable. However, in highly sheared zones, creep strains accumulate causing gradual strength degradation. As the process continues, the degrading envelope can reach the stress state in some locations and, then, in situ shear stresses decrease to be compatible with the ever-degrading failure envelope. Eventually, this condition occurs in a continuous zone and the slope fails due to tertiary creep. Tertiary failure under dry conditions has the form of an earthflow, as the soil mass above the slip surface suffers significant shear strains.
