An uncoupled procedure for performance assessment of slopes in seismic conditions

To assess the seismic performance of slopes, the simplified displacement-based methods represent a good-working balance between simplicity and reliability. The so-called uncoupled methods permit to account for the effects of deformability and ductility by computing separately the dynamic site response and the sliding block displacements. In this paper the procedure proposed by Bray and Rathje (1998) was revised and adapted to Italian seismicity on a set of subsoil models, representative of the different soil classes specified by the Italian and European Codes. The relationship expressing the decrease of the equivalent acceleration with earthquake/soil frequency ratio was then obtained by means of dynamic 1D seismic response analyses. Statistical correlations between calculated Newmark displacements, significant ground motion parameters and the critical acceleration ratio were also derived. To estimate the reference ground motion parameters necessary for the full implementation of the proposed procedure, literature predictive equations, calibrated on strong motion records of international databases, were revised for the Italian seismicity. These ground motion prediction equations, together with simplified displacements relationships, allowed for developing an original quick procedure to evaluate the seismic slope performance by specifying the probability of exceedance of a threshold displacement, based only on few seismic input motion parameters.