How it is done and how the Mont Blanc tunnel was built

Italy and France are connected by one Gallery about 11.6 km long which pierces the Mont Biancothe highest peak of the Alps and all over Europe. Hidden inside the mountain, the structure of the tunnel allows the transit of entrance and exit vehicles from Italy, By means of a single lane road structure by direction. Its travel, in compliance with the currently imposed speed limits, is of about 12 minutes. In this article we discuss its history from a technical point of view, starting from excavation operations to current security and surveillance systems present.

The geometry of the Mont Blanc tunnel

As you can observe from Google Maps (image below), the tunnel follows an almost rectilinear trendconnecting Charmonix (Haute Savoie, France) with Courmayeur (Valle d’Aosta, Italy). The work was built through structural elements characterized by A subdivision into Councils (ie “pieces“, vulgarly) approximately long 29 m each one. Thus considering its entire length, you reach a number of councils equal to 400coming to the approximately 11.6 km before mentioned. It is a tunnel to “cane“Single, that is, in which A single tunnel provides support for both directions.

The construction began in 1959however staggered between the two extremes: in Italy it started in January, while in France in June of the same year. The completion of the excavation took place on August 3, 1962, while the actual inauguration took place in June 1965. Although it may seem to be all stuck and made in sufficiently short times, it must be considered that The first design proposal of the tunnel dates back to 1908in which 4 different crossing geometries were offered.

The tunnel develops, as can be seen from national borders, for about 1/3 on Italian territory. The remaining 2/3, on the other hand, develop on French territory.
The height of rocky material on the vertical is greater than 2000 m for more than half a length of travel. The Italian entrance is at 1381 m altitude, which become 1274 m in the French entrance. In the middle of the gallery, the maximum height recorded is about 1400 m. The difference in height of 107 m is won in its length, generating an average slope of about 1%.
The roadway is a total of 7 long, as mentioned, a lane for a direction of travel. The thickness of the flooring structure (overall with the structural part) is 80 cm. Below this thickness we find some channels at the service of the tunnel safety conditions:

• A channel is dedicated toNutrition of the gallery through pure air (that is, taken from the outside and widespread in the circulation area by placing mouths every 10 m);
• A channel allows evacuation of the tunnel (you access it from the lateral emergency exits);
• A channel, twin in the previous one, allows the removal of the fumesthrough suction mouths arranged per 100 m;
• A channel is dedicated to Protection of the fire conduct in which water circulates.

The whole gallery is physically confined from the ground above through A classic arched structure which ends in the base part, intersecting with these channels now mentioned, separated from the physical roadway by thicking 80 cm flooring (overall finishes).

The tunnel was excavated mainly with a series of air perforation machines tablet. Initially, excavation activities proceeded to 8-10 meters per day. However, reaching more internal layers of the mountain, these processes have undergone varied slowdowns for the difficulties encountered following the perforations. In fact, several collapses have followed each other on the Italian side, causing in some cases even victims. The problem of infiltration of underground water in the excavation itselfalso this source of delays in the roadmap.

Other internal services and security systems

Like any tunnel, the Mont Blanc tunnel is also equipped with internal security elements, dedicated to reducing risks during the travel. In particular, in the 11.6 km of development, the gallery is equipped with 18 parking pitches For each sense of circulation, one every 600 m. Each pitch is large 3 me extends for 30 m. They are also present 116 niches sos Located, alternatingly, every 100 m in the two senses of travel. For protection against extreme events, such as fires or propagation of fumes, they are present 37 connection points to emergency exitsthat is, to the evacuation path described first. At each point, an audio/video dissemination system allows the communication of messages with users.

In the entrance areas to the tunnel, both France and Italy side, there are several preliminary services to access: it starts from binational police services, up to those of reception to customers (info point). There is no shortage of refreshment areasthe charging columns for electric vehicles and parking lots. In both senses, in relation to the part of the entrance to the tunnel, there are also i toll systems.

The 1999 accident and closing

Historically, this infrastructure is also sadly known for the events that occurred in 1999, or the fire that developed inside the gallery that caused 39 victims. The huge damage of the accident is also due to the important quantity of fuel material present inside the gallery at the time of the fire of the fire, although the victims were caused by the release of cianidric acid (developed by the combustion of the insulation material of a truck with a refrigerator cell). Unfortunately, the sentence of the process led to light a series of deficiencies in the ventilation system and in the refuges and safety standards implemented That could perhaps have contained the damage: this caused a closing of the tunnel for about three years, necessary to integrate/restore safety measures with further fire niches and new rescue places.