Italy

Brenner Base Tunnel: First Breakthrough at the Isarco River Underpass

After months of preparation on the Isarco River Underpass construction site, the excavation started in early October 2020. The excavation works in this southernmost construction lot of the Brenner Base Tunnel were preceded by highly complex ground freezing.

Brenner Base Tunnel, Isarco River Unerpass: Start oft he excavation works in October 2020
Credit/Quelle: BBT SE

Brenner Base Tunnel, Isarco River Unerpass: Start oft he excavation works in October 2020
Credit/Quelle: BBT SE

Starting from one of the four shafts built on the Isarco River Underpass construction site, the underlying aquifer and alluvial deposits below the riverbed were frozen by injecting liquid nitrogen into a closed circuit of “freezing tubes” below the level of the river. The liquid nitrogen, running through the tubes at a temperature of -196 °C, subtracted heat from the surrounding soil, thus freezing the water within the soil and dropping the ground temperature to -35 °C. To maintain this low ground temperature during the excavation work, a type of brine is circulated in the cooling circuit. This procedure solidified the loose material below the riverbed and excavation work began on 5 October.

  The first breakthrough through the frozen soil under the river Isarco took place on November 6, 2020.

Credit/Quelle: BBT SE

The first breakthrough through the frozen soil under the river Isarco took place on November 6, 2020.
Credit/Quelle: BBT SE

First of Four Tunnel Breakthroughs Took Place on November 6

The first breakthrough through the frozen soil under the river took place on November 6, 2020. After excavating 59 m the first rock face southwards, towards the Station in Fortezza, was broken through using excavators and hydraulic hammers.

This was the first breakthrough of a total of four tunnels running under the Isarco river. The Brenner Base Tunnel will be connected to the existing railway network, i.e. two connecting tunnels will be built in addition to the two main tubes. These connecting tunnels with a total length of 1500 m will provide the link to the existing line and to the station in Fortezza in the future.

The ground freezing technique made it possible to avoid re-routing of the river crossing the Brenner Base Tunnel route, thus reducing the impact on the environment, especially on the fish population in the Isarco river.

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