Disg Seminar Series - Rostisciani, Verrucci

Lunedì, 26 Gennaio, 2015

Giada Rotisciani, Modeling of water infiltration in unsaturated soils

A deep knowledge of the hydro-mechanical behavior of unsaturated soils is needed to predict
phenomena, such as foundation settlements, shallow landslides or embankment instabilities, due to
rainfall events. For this, the response of a horizontal soil layer under wetting conditions was
numerically studied using a finite element code. The consequences of the imbibition process were
described and analyzed, focusing the attention on the stress paths followed by different points inside
the layer, the ground surface settlements and the propagation of the wetting front through the soil. The
mechanical behavior of the solid skeleton was described using an elasto-plastic constitutive model
formulated in terms of effective stress and extended to unsaturated conditions. The model was
calibrated considering laboratory-scale experimental results under suction-controlled conditions for
two real soils with different physical and mechanical properties. Moreover, the predictive capabilities
of the model were evaluated by simulating a centrifuge test conducted on a small-scale embankment
made of sand-clay mixture. During the test the embankment was inundated and the time evolution of
the crest settlements and the spatial distribution of the void ratio were monitored. The comparison
between the numerical predictions and the centrifuge data showed that the model was capable of
accurately describing the hydro-mechanical response of the soil resulting from the capillary rise.

Luca Verrucci, Effects of cavities on seismic ground response
Within the studies about the topographical and morphological effects on the earthquake ground
motion, the interest is growing whether the motion could be locally influenced by the presence of
natural and anthropic cavities. To this aim analytical models and 2D numerical analyses suggest that
amplifying effects on the horizontal component are expected above the flanks of the cavities while
attenuation effects are expected in the zones overshadowed by the cavities. A set of 2D numerical
analyses performed with a finite difference code were performed to investigate the importance of the
main factors involved in the diffraction of seismic waves by a cavity: size and embedment depth,
prevalent wavelength of the incident motion and incident angle. Some simplified amplification/deamplification
charts have been obtained in terms of dimensionless parameters. A numerical insight on
the boundary conditions simulating a plane wave front is proposed.

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