Acquista:
Nei progetti di gallerie in ambito alpino o peri-alpino, la stima degli impatti delle opere sugli acquiferi costituisce un aspetto che ha importanti ricadute di tipo socioeconomico. Tali impatti sono principalmente riconducibili al drenaggio delle acque in galleria, con conseguente abbassamento del livello piezometrico di falda e riduzione o persino azzeramento della sua produttività, con conseguente disseccamento di pozzi e sorgenti. In taluni contesti, l’abbassamento piezometrico può avere conseguenze negative anche dal punto di vista geotecnico, potendo provocare cedimenti in superficie tali da mettere in pericolo strutture e manufatti preesistenti. La caratterizzazione preliminare di questi impatti è importante perché consente, da un lato, di predisporre soluzioni di mitigazione atte a minimizzarli, dall’altro lato di programmare in anticipo misure adeguate di compensazione per i territori e le comunità coinvolte. Per questo, per il progetto delle gallerie della nuova linea ferroviaria AV/AC Milano- Genova sono stati pianificati e compiuti studi idrogeologici accurati e sistematici, mirati a valutare accuratamente l’entità degli impatti attesi sugli acquiferi potenzialmente interessati dalle opere. L’articolo illustra i criteri seguiti per impostare questi studi e i risultati raggiunti.
Hydrogeological studies for designing the High Speed/
High Capacity Milan-Genoa railway line underground
works - Assessment and mitigation of the tunnnelling
impacts on the existing aquifers
In design of tunnels in the Alpine or peri-
Alpine area, assessment of works impacts
on aquifers is an aspect with important
socio-economic repercussions. These impacts
are mainly due to the drainage of
water into the tunnel, resulting in lowering
of the groundwater level and reduction
or even zeroing of the productivity, with a
consequent drying up of wells and springs.
In certain contexts, groundwater lowering
may have negative consequences in terms of geotechnical, being able to cause surface
subsidence such as to endanger existing
structures and buildings.
Preliminary characterization of these impacts
is important because it enables, on
the one side, to prepare mitigation solutions
to minimize them, on the other side to
program in advance the appropriate compensatory
measures for the territories and
communities involved.
For this, for the design of the tunnels of the
new high speed/high capacity Milan-Genoa
railway line we have planned and made detailed
and systematic hydrogeological studies,
targeted to accurately assess the extent
of the expected impacts on aquifers potentially
affected by the underground works.
The studies have been developed through
two steps: in a first step we tried to identify
the areas in which excavating the underground
works would cause most likely
important impacts on aquifers, in a second
step, for the areas with the greatest probability
of impact, studies have been refined
with numerical flow models aimed to assess
the local impact and distribution patterns
on existing water resources.
An example of this is represented by the
studies carried out for the Cravasco access
tunnel. The geognostic surveys performed
and monitoring of groundwater levels have
made it possible to reconstruct a detailed
geological-hydrogeological context. The
subsequent development of a numerical
model of the same has allowed to assess in
advance the impact that drainage caused
by the access tunnel excavation could determine
on water resources and on the existing
surface drainage network. Using the
same model is finally possible to arrive to
a reliable assessment of the likely inflow
of water inside the tunnel, both transient
(during tunnel excavation) and steady (during
operation).
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