Underground engineering

BBT: Mules II and Mules III

Brenner Base Tunnel
Owner/client Brenner Basistunnel BBT SE
Type of service Detailed Design; Safety Coordination Design
Location Brenner
Period 2013 - present
Cost € 1.400.000.000

PRO ITER Prog. Infrastr. Terr. (40%); Pini Swiss Engineers SA; Poyry Schweiz AG; Pasquali-Rausa Engineering

The Brenner Base Tunnel is the key element of the new Brenner railway line between Munich and Verona. With its 64 km, it will be the longest underground railway connection worldwide.

The project involves the detailed design, the safety coordination design and the construction of the lots Mules 2 and Mules 3 of the Brenner Base Tunnel, in the stretch between the Northern national border (approx. km 32.0+00) and the adjacent lot 'Underground Crossing of the Isarco' (km 54.0+00 Eastern pipe).

The Brenner Base Tunnel system consists of two one-track parallel (at a distance of 40-70 m) railway tunnels and a service tunnel, which during excavation shall be used as an exploration tunnel. In terms of layout, the service tunnel is located between the two main pipes, 12 m lower than the main axes; only close to the South entrance (from km 51.6+00), the service tunnel deviates from its central position, and is no longer aligned with the line tunnels as far as the Aica entrance.

Main Axis

2 line tunnels (main axes), approx. 22 km.

Exploration tunnel

1 service/exploration tunnel, approx. 16 km.

Cross tunnels

69 cross tunnels with an overall length between 40 and 70 meters.

Emergency stop

1 emergency stop with relevant connection and ventilation tunnels, an access tunnel and a central tunnel (approx. 4500 km).

Carriageable window

1 carriageable window for connection with the outside (approx. 1700 meters).


3 chambers to assemble the TBM

Approx. at km 44.7+00 there shall be an emergency stop (L=530 m) with relevant connection and ventilation tunnels, which shall be used to manage emergency situations in case of fire. The stop is connected to the outside by means of a carriageable tunnel that runs parallel to the line tunnel for approx. 5 km and subsequently comes out onto the Mules window (L=1720 m), which connects the work to the outside.

The tunnel system is completed by cross tunnels that, besides providing an escape between the pipes (one approx. every 333 m), also host the technical rooms and the fire-fighting tanks. For plant-engineering and hydraulic purposes, approx. every 2000 m there shall be vertical shafts for connection of the cross tunnels with the underlying service tunnel. Close to the Mules window entrance there shall also be an underground ventilation station, directly connected to the outside by means of a shaft (H=60 m).

From a geological point of view, the Brenner Base Tunnel develops across the main tectonic units forming the Alpine chain, with a maximum overburden of 1700 m. These units, which consist of several overlapping layers, are what remains of the collision between the European plate and the Adriatic (African) one; in the design area they form a dome, at the center of which it is possible to identify the Pennidic and Subpennidic units of the Tauern window, i.e. the deepest tectonic units that form the core of the Alps. Southward, the Brenner Base Tunnel crosses the fault zone that forms the Periadriatic Lineament, of regional relevance, which separates the Austroalpine basement from the Southern Alpine one.

The line tunnels show several applied typical sections, which vary based on both the excavation method (in part using traditional methods, but mainly with the TBM) and the number of tracks (close to the adjacent lot 'Underground Crossing of the Isarco' both tunnels become two-track and three-track).

From the geological point of view, the Brenner Base Tunnel crosses, with maximum overburdens of the order of 1700 m, the major tectonic units that make up the Alpine chain.