The Isarco underpass construction lot is the southernmost part of the Brenner Base Tunnel before the railway station in Fortezza and it is located 1 km north of the town of Fortezza, in the Prà di Sopra neighbourhood.
The works on this construction lot began in October 2014 and should take about 8 years to complete, ending in November 2022. The contract awarded to RTI Salini-Impregilo S.p.A., Strabag A.G., Strabag S.p.A., CCC Soc.Coop. and Collini Lavori S.p.A. is worth 301 million Euro.
The contractor is currently carrying out a series of tests on a specific area, the so-called test field, in order to verify the characteristics and reactions of the soil when it is subjected to a series of fluid injections. The technical name for the process is "jet grouting" and it is a consolidation technique to improve the geotechnical characteristics of the soil.
For the actual underpass of the river, ground freezing techniques will be employed. This environmentally friendly technique consists in freezing the water in the ground itself by circulating a liquid, such as nitrogen or brine, at extremely low temperatures in the soil to be consolidated. The freezing process improves the mechanical characteristics of the ground, thereby eliminating the need for further actions to improve ground stability. Once consolidation is complete, excavation will take place as is usual for underground full-bore tunnels.
To carry out this cutting-edge - and very delicate - process, a series of activities are required to carry out the individual work phases in an orderly and efficient manner and with the smallest possible degree of environmental impact. These activities include the re-routing of the Brenner state road SS12 near the Fortezza sports field and the building of a new road. Besides this, a loading/unloading area will be built near the southern lane of the A22 highway for the set-up of the future construction sites for this lot.