Abstract
The effects of sites and plasticity index (Ip) on the inherent strength anisotropy of eleven different clay deposits are quantitatively examined by the unconfined compression test using a small size specimen with a different angle of inclination to the vertical. A new method for a slope stability analysis, taking the effects of the IASIA method (Inherent And Stress Induced Anisotropies) into consideration, is proposed. The applicability of the IASIA method and the optimum embankment design are examined through case histories of embankment failures on soft soils. The undrained strength anisotropy cannot be estimated by parameters such as the Ip value because of the complicated relationship with the factors influencing undrained anisotropic strength. It must be directly measured. The IASIA method was recommended from a study of a failed embankment. The probability of failure (Pf) and consumer's risk (Pc) from half of the unconfined compressive strength (qu/2) were (2.5~25.5)% and (4.7~42.3)% less than those of the Iwai qu/2(IASIA) and Urayasu qu/2(IASIA). Therefore, the design results were underestimated by disregarding strength anisotropies. If, Pf and Pc were considered, the Ct values increased. However, the Pc values drastically decreased to 24.8% from 54.3% concerning the 75-mm sampler and n increased, thus avoiding latent risks. These mean that the IASIA method can be used for optimum embankment design based on performance provisions.
