Simplified method for evaluating seismic stability of steep slopes

Steep slopes composed of weakly cemented granular soils are common along the Pacific Coast of North America. These slopes, standing at angles of 30° to near vertical, are observed to be prone to seismically induced failures. The steep topography of these slopes makes them particularly susceptible to amplification of seismic waves, and the brittle nature of these materials make deformation-based stability analyses inappropriate. In this paper, a simplified method is presented for assessing the seismic stability of these slopes, utilizing average seismic coefficients to account for the effect of topography. This procedure is based on a review of field and laboratory observations, as well as analyses carried out using generalized consistent transmitting boundaries. The results of the analyses indicate that the amplification due to the soil column in the free field behind the crest dominates the response. The amplification due to topography, on the other hand, shows little variability, and is on the order of 50%. The proposed procedure presented herein gives practicing engineers a method to conduct stability analyses that better represents the actual field conditions for these steep, brittle slopes.

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