The Periadriatic Seam: a unique aspect of the BBT project

Constructing the Brenner Base Tunnel means overcoming a great number of challenges, and among them is the crossing of the Periadriatic Seam within the Mules 2-3 construction lot, the largest of the entire BBT project. We spoke with David Marini, Engineering Manager for the Brenner-Fortezza stretch.


Mr Marini, what is the Periadriatic Seam, or Line, and why is it important in the context of the construction of the Brenner Base Tunnel?

The Periadriatic Seam is the longest fault zone in the entire Alpine region: it is 700 kilometres long and it intersects the route of the Brenner Base Tunnel at Mules for approximately 700 metres within the Mules 2-3 lot. The Periadriatic fault separates the Southern Alps from the Eastern and Western Alps, respectively.


When was the exploratory tunnel excavated in this fault zone, and for what purpose?

The exploratory prospection work in this fault zone was carried out between April 2012 and May 2014 with the aim of gathering useful information about the rock mass and its behaviour. This allowed us to significantly reduce uncertainty and possible risks during the excavation of the main tunnels.


How extensive was the fault zone, according to initial predictions?

The extent of the fault zone was initially estimated at approximately 500 metres, based on information available from surface geological mapping and deep boreholes carried out from ground level.

During the excavation of the exploratory tunnel, we were able to acquire a wealth of additional geological, geotechnical and hydrogeological data, as well as discover the exact extent of the fault zone, which turned out to be almost 300 metres longer than originally expected.


What rock formations are to be found in the area of the fault zone?

This fault zone runs between the Brixner granite formation to the south and the undifferentiated Austroalpine polymetamorphic basement to the north. The overburden in this area is between 500 and 700 metres.


What did the opportunity to work on and explore this specific feature of the BBT project mean for you?

There are certainly many challenges in the construction of our tunnel, and the crossing of the Periadriatic Seam is only one of them.


Since this is a geological fault zone where the Eurasian and Adriatic plates meet, working in this area has been a very significant technical challenge for me, and I feel safe in saying that the same goes for all the professionals involved.



We would like to thank Mr. Marini for the valuable information on the Periadriatic Seam and the exploratory tunnel. His remarks well describe the context in which the Brenner Base Tunnel is being built. This is a crucial project for European mobility, as well as an infrastructural work of considerable technical complexity.