The interaction of seismic waves with step-like slopes and its influence on landslide movements
Résumé
The interaction of seismic waves with slopes is a major factor influencing landslide movements that involve slope stability, local site seismic amplification and topographic effects affecting ground motion. The results of a numerical study of landslide movements induced by the interaction of seismic waves with step-like slopes are presented here. To investigate this input-slope interaction, a dynamic analysis was performed using the finite difference stress-strain numerical code FLAC 6.0 under visco-plastic conditions. The dynamic signals were selected to be representative of different peak ground accelerations (PGAs), Arias intensities and frequency contents, and they were used in a parametric study of different step-like slopes with different geometrical configurations in terms of dip, height and thickness of geological strata. The derived outputs
were processed for a seismic amplification analysis and to evaluate the induced stress-strain effects in terms of progressive failure and resulting displacements. The obtained results: i) describe a fundamental role of topography in amplifying or de-amplifying the seismic ground motion; ii) demonstrate that the progressive failure of unsheared slopes influences the seismic amplification; iii) show that the strain effects on unsheared slopes, in terms of progressive failure, are more intense with increasing Arias intensity and slope dip; iv) prove that amplification or de-amplification processes can justify the values of displacements involving pre-existing landslide masses,which are significantly differentwith respect to those expected on the basis of sliding block approaches (i.e., Newmark's and flexible sliding block methods); v) highlight that, in the geological setting considered here, the seismically induced displacements arising from the
reactivation of pre-existing landslide masses can be significantly underestimated by sliding block approaches in the case of low-angle slopes characterised by high K values, i.e. the ratios between the critical pseudostatic threshold (ky) of the landslide and PGAs of the applied seismic input.