Autore: Enrione Riccardo

Titolo: "Costruzione dello scenario idrogeologico nel progetto di gallerie: il caso della galleria di Montanara (Autorstada AT-CN)"

Politecnico di Torino. Ing. Ambiente e territorio

Abstract in inglese

Hydrogeological scenery construction in tunnel project

the montanera tunnel case (At-cn motorway)

The safeguard of groundwater quality and quantity has become, in the last decade, a remarkable problem in engineering concerns. That has been triggered by the potential exhaustion consciousness of the groundwater resource, once considered a renewable property and so of poor value. Moreover, continuous technological evolution and territory intense exploitation can only make worse the damage inflicted on the groundwater reservoirs that, therefore, have to be protected.

Among the aspects regarding these topics there is the one concerning the interaction between engineering works and the aquifers interested by the works themselves. Furthermore, considering the growing demand for underground structures, finalised to the improvement of life quality, it turns out clearly how these topics are absolutely actual.

The interaction between underground works and aquifers has been always source of considerable hydrogeological difficulties. The lack of environmental feasibility studies, prior to the final study, has been often the reason of remarkable hydrogeological accidents.

Among the various infrastructure interesting the underground there is one of particular design importance and, at the same time, of considerable impact from the hydrogeological point of view: the tunnel. Considering the lack of sensitivity about this topic, a proper study has been developed with the intention of provide the essentials methodological proceedings required to make out the difficulties connected to the aquifers protection.

The leaded study has involved a portion of the non-confined aquifer located in the western sector of the Cuneese plain, on the right orographic bank of the T. Stura di Demonte (Stura di Demonte stream), included in the Montanera, Consovero e Ceriolo communes. The area extends for 15 km² and it’s principally characterised by two geo-morphologic elements: the main Cuneese plain level and the alluvial terrace; this last one is the actual connection device between the main plain level and the bottomland band hosting the T. Stura.

The selection of the area to investigate is due the particular engineering interest that it exerts as it is involved in the Motorway AT-CN executive project that takes in consideration the construction of a tunnel in the NE zone off the Montanera town.

Preliminarily has been leaded a geo-morphologic study, that has permitted a first making out of the research area by numerous on-site investigations and geological survey. Once these rough data has been acquired, a wide hydrogeological study has been developed on regional scale as well as on site scale.

The outlining of the hydrogeological scenery has allowed the identification of the hydrogeological complexes, the working out of the actual flow field and the evaluation of the aquifer hydrodynamic parameters.

That has been made possible by the setting up of an acquisition campaign of the water levels inside piezometers and by four different acquifer tests (Lefranc, variable head slug test, constant head slug test and two classical long-term aquifer tests) .

On the bases of the results achieved through the studies described above, a finite difference numerical model has been implemented, capable to simulate the groundwater flow in completely saturated porous media (Modflow 98, in the version implemented in the GMS environment: Groundwater Modeling System).

Such tool has allowed the reconstruction of the actual dynamic of the aquifer flow field and, successively, the simulation of the effect of the Montanera tunnel presence on the territory. By so doing, every possible hydrogeological difficulty, related to the tunnel construction, has been identified, the effects have been quantified and possible resolutive scenarios have been proposed.

In short, the elaboration results have shown the fundamental role that a proper hydrogeological study holds in seat of feasibility project of an engineering work. Moreover, has been brought out the value of the aquifer numerical modelling as a precious tool at the service of the groundwater quality and quantity.