Mixed finite element analysis of a trial embankment at the coastland of Venice, Italy
N. Castelletto, P. Teatini, M. Ferronato, G. Gambolati
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
L. Tosi
Istitute of Marine Sciences, CNR, Venezia,
Italy
ABSTRACT
In the safeguard works currently under way at the inlets of the Venice Lagoon,
an instrumented trial embankment was built with the aim of investigating the lagoon subsoil
response to loading/unloading and assessing the relevant geomechanical parameters. A 20 m
radius, 6.7 m high vertically-walled sand cylinder was constructed on the Venice littoral from
September 2002 to March 2003, and removed in June 2007. The movements of the ground surface
were accurately monitored at the center and side of the embankment, as well as at a reference
benchmark 100 m apart by leveling, GPS, and persistent scatterer interferometry. Moreover, cone
and standard penetration tests, geotechnical borings, and standard lab tests were performed to
characterize the soil below the embankment. This large amount of information is used to set-up
a fully coupled three-dimensional (3D) mixed finite element (MFE) model based on the Biot consolidation
equations. Linear piecewise polynomials and the lowest order Raviart-Thomas mixed
space are selected to approximate the medium displacement and the fluid flow rate, respectively.
The approach ensures an element-wise mass conservative formulation while preserving
the practical advantage of low-order interpolation elements. This helps to stabilize the numerical
solution and obtain a more accurate calculation of the flow field. A finite difference scheme
is used for the integration in time. The model is implemented over the actual lithostratigraphy of
the subsurface down to 60 m depth by prescribing the surface loading vs time as a forcing factor.
A small adjustment of the geomechanical and hydrological parameters allows for a satisfactory
reproduction of most of the observed displacements both in the vertical and horizontal directions
despite the simple linear elastic constitutive law used in the modelling approach.
