Environmental Engineering Reference
In-Depth Information
frequent flooding of the city of Venice together with or instead of the MOSE
(Experimental Electromechanical Module) project. This is an ambitious plan now
under construction involving massive gates located at the three inlets of the lagoon
that will rise from the sea bed to cut the lagoon off from the open sea when the
forecast tides exceed a safety limit. MOSE is controversial, however, on the grounds
of cost, effectiveness and environmental impact. Increasing the surface elevation by
fluid injection has some appealing aspects. In their original proposal [COM 2003], it
consists of the injection of anthropogenic carbon dioxide or, alternatively, seawater
in a brackish, sandy aquifer lying 600-800 m under the lagoon of Venice. The effect
expected is the uniform uplift of Venice and its hinterland by up to 30 cm in 10
years (see Figure 5.24), i.e. returning to the 1908 level (see Figure 5.2). The main
problem is how to obtain a uniform uplift pattern to avoid the possible generation of
cracks in historical buildings due to differential vertical displacements. These
buildings have already undergone all admissible differential settlements, i.e. they are
in a limited state because of the building technology, foundations and past history.
Additional differential settlements, even if small for a sound building, could have
serious consequences for many.
Figure 5.24.
Expected uplift (cm) in Venice after 10 years of fluid injection,
redrawn with permission from Comerlati et al. [COM 2006]
When CO
2
is used, it is supposed to be injected through 12 vertical wells into the
aquifer, which is confined by a 25 m thick impervious cap rock. The average
temperature in the aquifer is 28°C and the average pore pressure is 70 bar. It is
proposed to reduce CO
2
in the subcritical condition close to the critical point with an
overpressure of 10 bar around the wells. As discussed in [SCH 05], a phase change
of CO
2
cannot be avoided because of the prevailing ambient conditions at the
chosen depth and the injection pressure needed, which is above the critical value.
