Modified Newmark Model for Seismic Displacements of Compliant Slopes

Newmark sliding block analyses are widely used for estimation of permanent displacements of slopes in earthquakes. The conventional Newmark model, however, neglects the dynamic response of the material above a potential failure surface. Decoupled procedures have been developed to account for that response, but they neglect the effects of permanent displacements on the response. A modified Newmark analysis that considers the dynamic response, including the effects of permanent displacements, of the material above the failure surface is presented. The modified Newmark analysis shows that the decoupled approach produces somewhat conservative estimates of permanent displacements for stiff and/or shallow failure masses, but that it may produce unconservative estimates for failure masses that are soft and/or deep. Many slopes of large, lined landfills may fall into this latter category. The notion of a slope spectrum, which illustrates the effect of the natural period of a potential failure mass on permanent slope displacement, is also introduced.