In the town of Fortezza works on the Isarco River Underpass construction site, which is the southernmost construction lot of the Brenner Base Tunnel, are proceeding at full speed. Two 25 m deep shafts have been excavated, on both sides of the Isarco river, which are located on the new tunnel route.  

The complex freezing procedure has already been used for the first connecting tunnel below the Isarco river.  Now the ground below the river will once again be artificially frozen to allow the start of the excavation works for the first ‘main’ tunnel below the Isarco river.  

The groundwater is frozen, starting from the shafts by circulating a refrigerant fluid inside the soil through special heat exchangers. As a first step, liquid nitrogen is injected into this in a closed pipe circuit below the riverbed - the refrigerant substance has a temperature of -196°C and is then dispersed into the atmosphere as a gas. The next step is about maintaining the temperature between -30°C and -35°C by using saline brine, so that the ground stays frozen allowing the excavation works for the Underpass to proceed. 

This highly complex procedure was deemed necessary, to avoid relocating the Isarco river from its original riverbed. The significant advantage of this freezing procedure is that there is less environmental impact on this the second longest river in the Alto Adige. This ensures that the diversity of flora and fish fauna is preserved. For further information please click here, at/16 and it/103 for the tunnelbuilder archive and also visit https://www.bbt-se.com/en.  11/21.