Nonlinear Numerical Simulation of the Soil Seismic Response to the 2012 M-w 5.9 Emilia Earthquake Considering the Variability of the Water Table Position

摘要

This research is focused on the case study of San Carlo village (Emilia-Romagna, Italy), struck by the 20 May 2012 M-w 5.9 Emilia earthquake that caused severe damage because of widely observed soil liquefaction. In particular, it investigates the influence on nonlinearity effects of the variability of the water table depth caused by seasonal fluctuation. The one-directional propagation of a three-component seismic wave (1D-3C approach), in a multilayered soil profile, is simulated using a finite-element model and an elastoplastic constitutive behavior with hardening for the soil (Iwan's model). The nonlinearity is described by the normalized shear modulus decay curve obtained by resonant column (RC) tests. The shear modulus is corrected during the process (Iai's model) to consider the cyclic mobility and dilatancy of sands, depending on the actual average effective stress and the friction and dilatancy angles obtained from cyclic consolidated undrained triaxial (CTX) tests. Profiles with depth of maximum excess pore water pressure, horizontal motion, and shear strain and stress are obtained in the case of effective stress analysis (ESA), for an average position of the water table depth and for a variation of +/- 1 m, and then compared with a total stress analysis (TSA). The variability with the water table depth of soil profile response to seismic loading is observed also in terms of hysteresis loops, time histories of the ground motion, and excess pore water pressure in the liquefiable soil layers prone to the cyclic mobility process.