Environmental Engineering Reference
In-Depth Information
Figure 5.6 shows the subsidence recorded along the same leveling line from
1952 to 1969 (a) and from 1973 to 1993 (b), allowing for an evaluation of the
surface lowering trends as a function of pumping time history.
5.1.4.2.
Subsidence of Venice: the mathematical model
An axisymmetric model has been used for the numerical simulation of the
problem. This implies the same symmetry conditions hold for the horizontal
stratigraphy, the central exploitation area (Marghera), the material properties and the
boundary conditions. By taking into account the spatial distribution of the active
wells, it seemed more realistic to consider the source points distributed over a
central circular area with a diameter of 3.0 km. This hypothesis is confirmed by
observing the piezometric contours of the aquifers considered (see Figure 5.7). It
also resulted in a close matching of the subsidence values measured and calculated
in the central area of the model.
Figure 5.7.
Piezometric surface of the fourth aquifer
The first finite element discretization used is shown in Figure 5.8a, where the
idealized geological stratigraphy can be seen [LEW 78]. In Figure 5.8b, a finer mesh
is presented that has been used in a second analysis within a parallel computation
procedure [SCH 99]. In both cases, isoparametric parabolic elements have been used
for both pressures and displacement interpolations.
