SURFICIAL STABILITY OF COMPACTED CLAY - CASE-STUDY

The factor of safety for surficial stability is highly dependent on th e effective cohesion. This study shows that even when triaxial tests a re performed at effective pressures as low as 13.8 kPa (2.0 psi), the results may still provide effective cohesion intercepts that are too h igh. The reason is that the compacted sandy clay behaves as an overcon solidated soil, with effective stress paths bending to the right with low to negative A-values. As demonstrated by this case study of a surf icial failure, the calculated factor of safety was 1.33 using the extr apolated value of effective cohesion of 5.3 kPa (110 psf). An unconfin ed submerged triaxial test resulted in a lower effective strength enve lope, which provided a factor of safety of 0.97 for the surficial fail ure. There are two factors that can increase the surficial stability o f a compacted clay slope: aging and root reinforcement. For the surfic ial failure, the effect of aging was minor and root reinforcement was not a factor in this case, because the roots had not penetrated to a s ignificant depth at the time of failure.