Investigation of Lateral Stress Relief on theStability of PHI = 0 DEG Slopes Using Laboratory, Fracture Mechanics, and Finite Element Method Approaches

Total stress analyses of purely cohesive cut slopes utilize the undrained shear strength for slope stability analyses. These slopes can have an in-situ lateral earth pressure that is greater than the vertical pressure. Excavations into these materials results in expansion of the slope face due to release of confining pressure. When strains exceed that which can be internally absorbed through elastic deformation, failure planes or cracks may develop at the toe of the slope. However, conventional limit equilibrium methods of slope stability analysis do not account for the in-situ stress conditions or the development of shear zones or cracks that occur from lateral stress relief. Progressive failure of the slope may occur if internal lateral stresses are large enough to cause stress concentrations in front of the advancing toe cracks. Finite element methods using substitution methods reveal two distinct shear cracks at the toe of slope consisting of a horizontal and an inclined failure plane while a tension zone develops in the backslope region. The formation and extension of the shear cracks are strongly dependent on ko and they can extend to approximately 1/4 of the slope height due to initial lateral stress relief. Classical limit equilibrium solutions regarding the critical slope height have been revised to account for lateral stress relief. Analyses indicate good agreement with published case histories and they reveal how the shear zones propagate to create progressive slope failure in stiff clay slopes under total stress analyses