“A great work”: This is how people who worked for years at the project defined it. The Gran Sasso Highway Tunnel is Europe's longest double-barrel tunnel, ranking twelfth in the world. Each "barrel" includes two one-directional lanes.
Thanks to its construction, it was possible to connect the Tyrrhenian to the Adriatic, linking Latium to Abruzzo. Works began in the 60's, requiring huge investments. They ended after 25 years. Hundreds of men, and tonnes of explosive and machinery, were used for the tunnel's excavation, during which 11 people lost their lives.
Let's go through the story of the Gran Sasso Highway Tunnel, whose construction required a lot of resources, men and equipment, giving life to one of the main connecting roads used by car drivers and carriers travelling each day from Latium to Abruzzo.
The inauguration of the Gran Sasso Highway Tunnel
The Gran Sasso Highway Tunnel measures 10,175 metres. Works began on November 14, 1968, but the tunnel was inaugurated only on December 1, 1984. The official ceremony, attended by the Italian Prime Minister, at that time, Bettino Craxi, inaugurated the one-directional lane heading towards Teramo, between the Assergi and Colledara junctions.
In between these years, there were many years of work, but also interruptions also due to the economic crisis. From 1975 to 1982, excavation works on the tunnel were interrupted. Costs for the entire project amounted to approximately 1,700 billion Italian liras (nearly €890 million) - instead of the initially foreseen 80 billion Italian liras, due to unforeseen circumstances. .
In 1982, concomitantly with the works to build the second tunnel directed towards L'Aquila, works to build the underground labs of the Italian National Nuclear Physics Institute, began. This, in practice, was the second barrel of the Gran Sasso Highway Tunnel, opened in 1993. These labs are located on the same level of the A24 motorway, approximately 1,400 metres under the Gran Sasso massif. Labs can therefore be accessed directly from the road, through an underground junction.
The Gran Sasso Highway Tunnel: The Project
The Gran Sasso Highway Tunnel project, curated by Alpina S.p.A., commissioned by S.A.R.A. (Società Autostrade Romane e Abruzzesi) and built by CO.GE.FAR, was approved in 1963.
After 16 years of work, the first tunnel heading towards Teramo was opened: it was 1984.
After 9 years, the second tunnel also opened, with the National Gran Sasso Labs: it was 1993. The project took 25 years to complete.
Excavations: How they were done
The excavation area had a particular rock conformation. Sudden weather changes were also very frequent. Therefore, precision instruments and meticulous work methods were used, as also suggested by the results of the analysis that were carried out.
Excavations used huge amounts of explosive, mainly to create a "Pilot tunnel". Milling instruments and 7 arm-drilling jumbos were also put to work.
The excavation of a guiding tunnel was needed to test if the rocks would remain in place after the excavation. This preventive technique was used to promptly meet eventual unforeseen events caused during the main excavation works. The excavated passage was then covered with sprayed concrete and archings: i.e. temporary structures that acted as a base for blocks of rock, arches or vaults to be positioned. It was then stabilized with a poured concrete covering.
Where the faults crossed, sub-vertical drainage activities were carried out to see if there was water underneath, also using drills and the mid-section excavation technique.
The Gran Sasso massif, in fact, is made of limestone, permeated by aquifers, except for the part near Teramo, where marly, impervious rocks can be found instead.
Geologists carried out studies on these aquifers, but they resulted to be incorrect. In fact, at Assergi, towards Rome, a very serious accident took place: On September 14, 1970 the TBM, at Valle Fredda, pierced the aquifer behind the mountain rocks. The pressure took the exploration tunnel down, with water and mud filling the tunnel and flooding the lower part of Assergi. There were no damages to people or things, but the unforeseen event caused the interruption of works for almost two years.
How works were carried out differently for the two tunnels is also something that characterizes the Gran Sasso Highway Tunnel project: i.e. For the tunnel heading towards Teramo, excavation materials were transported by rail, while rubber-tyred vehicles were used, instead, in the one heading towards Rome.
The two tunnels communicate through underground passages, located 300/600 metres from each other, and closed with flameproof doors, used as emergency exits. A longitudinal ventilation system, currently the most frequently installed in double-barrel tunnels, is also present.