Influence of extent of remedial ground densification on seismic site effects via 2-D site response analyses

Abstract

Remedial ground densification techniques are widely employed in seismically active regions to mitigate geotechnical hazards and reduce the potential for damage to structures. These techniques can substantially modify the local soil conditions and the seismic site response characteristics of the profile. This study provides a quantitative insight into the local site amplification in remedially densified soils. Parametric site response analyses are performed using various subsoil conditions and extents of ground densification. The free-field site responses obtained with and without ground densification are compared using two-dimensional (2-D) finite element models. The results show that the frequency content of ground motions propagating in densified sites is modified, with a shift of soil response harmonics towards higher frequencies. When a densified crust is implemented with unimproved soft soil layers underneath, the PSAs at the ground surface are generally reduced, at frequencies between 5 and 10 Hz. However, the levels of de-amplification decrease as the depth of ground densification increases. In particular, the densification of the full depth of liquefiable soil layers leads to higher PSAs at the ground surface. The results presented provide a better understanding of the geometry and density of the improved zones that can lead to the amplification of ground surface motions in the frequency range of interest for building response, prior to investigating more complex problems that include soil-structure interaction.