The influence of cyclic behavior of soils on seismic response of natural slopes is frequently disregarded in the design procedure adopted in current practice. This is mainly due to the complexity of the numerical analyses required to reliably account for these aspects. In detail, the analyses which neglect the effects of earthquake-induced excess pore-water, and the consequent reduction of soil shear strength, could lead to an unsafe estimation of the seismic slope stability condition and of the magnitude of earthquake-induced permanent displacement.

Therefore, the need of simplified procedures devoted to the estimation of the effect of earthquake-induced pore-water pressure on the seismic and post-seismic stability condition of natural slopes is clearly evident.

In this paper such kind of procedure for natural slopes in clay soils is presented.

In detail, the paper describes a simplified procedure devoted to the estimation of the seismic stability condition and post-seismic serviceability of natural clay slopes accounting for the reduction of yield acceleration coefficient due to the possibly occurring increase in pore water pressures. The proposed procedure adopts an effective stress analysis. The occurrence of excess pore-water pressure is evaluated using an experimental-based pore-water pressure generation model. This model allows predicting the occurrence and assessing the magnitude of excess pore-water pressure starting from the knowledge of the earthquake-induced shear strain levels.

Focusing the attention on normally consolidated soils, the earthquake-induced shear strain is estimated using a decoupled approach which adopts literary available shear modulus reduction curves.

The displacement response of the slopes is estimated using a Newmark-type analysis modified to accomplish for the effect of the reduction of the yield acceleration coefficient due to the soil shear strength reduction.

The results of an extensive parametric analysis are also described in the paper. The obtained results show that the acceleration level induced in the slope together with the plasticity of the soil are the parameters mostly involved in the occurrence of excess-pore-water pressure. In the same time these parameters are those mostly related to the magnitude of earthquake-induced permanent displacements.