A coupled MFE poromechanical model of a large-scale load
experiment at the coastland of Venice
N. Castelletto
Dept. of Energy Resources Engineering, Stanford University, CA, USA
G. Gambolati, P. Teatini
Dept. of Civil, Environmental and Architectural Engineering,
University of Padova, Padova, Italy
ABSTRACT
A three-dimensional fully coupled mixed finite
element (MFE) model based on Biot's consolidation
equations is implemented to simulate the geomechanical
response of a large-scale 5-year long loading/unloading test
performed at the Venice coastland, Italy. The model uses
linear piecewise polynomials and the lowest order Raviart-Thomas
mixed space to represent the porous medium
motion and the groundwater flow rate, respectively. The
approach ensures an element-wise mass conservative formulation
while preserving the stability of the numerical
solution and providing at the same time an accurate calculation
of the flow field. With the aim of characterizing
the Late Pleistocene and Holocene deposits above which
the MoSE project, i.e. the mobile barriers to protect Venice
from acqua alta, is under implementation, a 20-m radius,
6.7-m tall vertically walled cylinder was built from September
2002 to March 2003 and removed in June 2007. The
maximum load exerted on the ground at the completion of
the building activity was 0.105 MPa. The land displacements
were accurately monitored at various depths, the
center and outer boundary of the embankment by sliding
deformeters, leveling, global positioning system, and persistent
scatterer interferometry. Moreover, in situ tests and
standard lab tests were performed to define the hydrological
and geomechanical properties of the soil underlying the
cylinder. The model addresses the actual lithostratigraph
of the subsurface down to 50-m depth below the embankment
and prescribes the land surface loading versus time as
an external source of strength. A hysteretic elastic constitutive
law, with the Young modulus E in the loading phase
between 2 to 36 Mpa according to lithology, a ratio s = 15
of loading to unloading cycle E, and a small adjustment of
the hydrological parameters allow to predict quite satisfactorily
most of the observed pressure behavior, together with
vertical and horizontal displacements.
