Stability and Failure Geometry of Slopes with Spatially Varying Undrained Shear Strength

Abstract

The influence of spatial variation in undrained shear strength is an important practical consideration for assessing the stability of excavations or natural slopes. Prior research has focused on slope stability in normally consolidated or lightly overconsolidated clays, commonly assuming that undrained shear strength (cu) increases linearly with depth but remains constant in the horizontal direction. However, depositional history, geologic settings, and variations in groundwater conditions may result in a strength profile that varies vertically and horizontally. A parametric study was performed to determine slope stability considering undrained shear strength that increases linearly with depth but exhibits an initial undrained shear strength at the ground surface that varies over horizontal distance—a relationship defined geometrically by an angle called the cu profile inclination (θ). The analyzed solutions are presented through charts of normalized stability numbers (Ns). The results demonstrate that increasing the shear strength gradient increases slope stability, but considerable differences in stability were found between cu profile inclinations. The importance of the cu profile inclination is significantly influenced by the observed failure and slope geometry.