Stability of Undisturbed Residual Soil Hill Slopes

The cut slopes of saprolitic residual soils in the Himalayan foothills often remain stable at very steep inclinations that are much steeper than critical failure slope angles predicted by stability analysis. It is often difficult to obtain undisturbed samples of these soils. Physical inspection shows natural weak cementing property of undisturbed saprolitic residual soil. In order to overcome the inability of standard sampling techniques to collect undisturbed samples of the fragile saprolitic residual soil from the hillslope surface, a procedure with a modified sampler is adopted in this research. The shear parameters of undisturbed samples thus collected as well as that of reconstituted samples of the same soil are determined in direct shear testing at different saturation levels. Stability analysis of the saprolitic residual soil hill slopes was carried out using both undisturbed and remoulded soil properties at different degrees of saturation which revealed a positive contribution of the cementing property of the undisturbed soil towards higher stability of hill cut slopes.