Simplified charts to evaluate settlements from seismic compression in dry loose sand

In dry loose sand, seismic cyclic loads can result in contractive volumetric strains (seis- mic densification or compression) that can induce damages to structures, infrastructures and life- lines, accordingly with post-earthquake damages of past events. In the present work, a procedure has been adopted to define simplified charts to predict the possible effect of the seismic compres- sion phenomenon in dry loose sand in terms of soil permanent settlements, to be applied in Seis- mic Microzonation (SM) studies in the perspective of seismic risk reduction. The adopted proce- dure estimates the volumetric strains starting from shear strains profiles calculated by parametric 1D site response analyses in which some key-parameters affecting the dry sand behaviour are varied: the relative density and shear wave velocity profile, thickness of the compressible sand layer and its non-linear behaviour, the depth of the seismic bedrock, the input motion amplitude and its frequency content. The proposed charts provide the estimation of settlements in function of the input PGA classes, depth of the compressible sand layer and relative density or, alterna- tively, shear wave velocity.