Laura Tonni

Adapting a Generalized Plasticity Model to Reproduce the Stress-Strain Response of Silty Soils Forming the Venice Lagoon Basin

A Generalized Plasticity model, originally developed for the analysis of sandy soil behaviour, is modified in order to properly simulate the stress-strain response of a wide class of non-active natural soils, forming the upper profile of the Venice Lagoon basin. The main modification consists in introducing a state-dependent dilatancy, which allows proper modelling of granular soils over a wide range of pressures and densities, fulfilling at the same time basic premises of critical state soil mechanics. Moreover, according to recent developments on the isotropic compression of granular soils, few adjustments are introduced in the plastic modulus expression. The approach is validated by comparing the model predictions with experimental data obtained from drained triaxial compression tests on natural and reconstituted samples of soils having different fine contents.

Seismic Stability Analyses of the Po River Banks

The Po River is the major Italian watercourse. Over half its length is controlled with embankments as protection measures against heavy floodings. Recently, the Italian Government has funded a project for the evaluation of the seismic stability of about 90 km of embankments of the Po River. The project mainly aims at the seismic stability analyses of the river banks, with assessment of local site response and evaluation of the liquefaction potential. Hundreds of geotechnical investigations within the study area were performed and the water level variations in the embankment and subsoil were investigated using piezometers. This paper describes the methodology and the main results of the analyses. The safety of 43 significant sections in static and seismic conditions was investigated using limit equilibrium analyses. Dynamic effects in the seismic condition were considered using the pseudostatic method. Local seismic hazard and effects of site conditions on the ground motion are taken into account in the definition of the expected seismic action. Eventually, the analysis results are summarized in a static and seismic stability map of the investigated area, a useful tool for the local Authority in the prevention and mitigation.

NUMERICAL SIMULATIONS OF LIQUEFACTION PHENOMENA AFTER EMILIA ROMAGNA (20 MAY 2012) EARTHQUAKE

Soil liquefaction has been observed worldwide during earthquakes with induced effects responsible for damage, disruption of function and considerable replacement expenses for structures. The May 20, 2012 M5.9 shock in Emilia Romagna (Italy), is one example of moderate earthquakes yielding extensive liquefaction-related phenomena. The paper provides an attempt to simulate the observed ground effects using a finite element (FE) approach. The study adopts a FE computational interface (OPENSEES PL) implemented in OpenSees and able to analyze the earthquake-induced threedimensional pore pressure generation. Credited non-linear theories are applied in order to take into account appropriate flow rules as to reproduce the observed strong dilation tendency and resulting increase in cyclic shear stiffness and strength. The interface simplifies the 3D spatial soil domain, boundary conditions and input seismic excitation definition with convenient post-processing and graphical visualization of analysis results including deformed ground response time histories. The possibility to simulate wave propagation adopting realistic boundaries is of particular importance and significance in order to realistically reproduce liquefaction behaviour.