A SLOPE STABILITY ANALYSIS CONSIDERING UNDRAINED STRENGTH ANISOTROPY OF NATURAL CLAY DEPOSITS

摘要

The effects of sites and plasticity index (I_p) 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 I_p 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 (P_f) and consumer's risk (P_c) from half of the unconfined compressive strength (q_u/2) were (2.5-25.5)% and (4.7-42.3)% less than those of the Iwai q_u/2_(iasia) and Urayasu q_u/2_(iasia). Therefore, the design results were underestimated by disregarding strength anisotropies. If, P_f and P_c were considered, the C_t values increased. However, the P_c 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.