Fully Softened Shear Strength at Low Stresses for Levee and Embankment Design

Abstract

Shallow slides in levee and other embankment slopes are usually controlled by effective normal stresses less than 12 kPa (250 psf). For first-time slides in fine-grained soils, the fully softened shear strength is frequently used to model the strength of embankment soils because it represents the shear strength remaining after the effects of overconsolidation, compaction, desiccation, or other strengthening processes have been removed because of wetting, infiltration, stress relief, swelling, and weathering. However, there is limited fully softened strength data at effective normal stresses less than 50 kPa (1,000 psf), so existing correlations in this stress range must be extrapolated. This paper presents new fully softened shear strength data at an effective normal stress of 12 kPa (250 psf) and recommendations for estimating and modeling the stress-dependent fully softened shear strength envelope directly or as a power function in stability analyses.