Engineer Tomasi, what does it feel like to build a tunnel?
Building a tunnel is a curious activity, one that binds all who do it into a special tribe.
There are jealousies and boasting, of course, but there’s also a commonality, and a constant poaching of best practices, design solutions and innovative materials. That’s probably logical given that what tunnels do, by definition, is connect people who while close often live in different worlds or nations. The excitement over the first Gotthard Tunnel, back in the 19 century, testifies to that: German, Swiss and Italian capital and workers built it, and it was hailed as a geopolitical event.
With the Valico project, we did not of course span national borders. The “Variante” does, however, mark a very major intervention in the national story, making the North-South axis of the peninsula a more efficient and closely-knit one.
That’s the function of tunnels, be it the 24.5-kilometer Laerdals Tunnelen in Norway, the world’s longest, or the once-huge-but-now-miniature tunnel built to link two palaces in Babylonia thousands years ago, not to mention the 711-meter passageway built to allow people to connect Naples and Pozzuoli in ancient Roman times.
How does the Valico Bypass compare with those iconic works?
All told the Valico Bypass is a 59-kilometer monument, and its 41 galleries, 41 new bridges reduce travel times by almost a third and save on fuel by drastically reducing the up-and-down topography of the route drivers now have at their disposal.
Engineers have long since perfected the art of boring from two sides of a mountain and connecting to make a tunnel. There’s a lot of art and science in that, but it’s no longer a major feat. The challenges of today have to do with coping with geologically volatile terrain – it’s harder to drill through the Appenines than the Alps, in fact – and with making sure that safety concerns and air circulation is achieved. These factors are largely invisible to the public but occupied a lot of our time and thought in this project.
The Variante won a lot of attention for the Sparvo tunnel, which used the world’s largest-ever tunnel boring machine to carve a tubular channel with a 200-square-meter section through 2.5 kilometers of earth with a very high level of grisou, known in English as firedamp. This methane-dominated gas has half the density of ordinary atmospheric air and as a consequence gathers in dangerously combustible pockets – which of course are constantly being opened in the process of drilling a tunnel. To be clear, the presence of firedamp is why miners used to bring canaries down into the coal mines.
Tell me more about this giant machine.
The boring machine, named Martina and boasting a 15.5-meter shield diameter that completed one full Sparvo passage in less than a year, had to be equipped with explosion protection, developed with the help of local universities, that consisted of giving a double-wall and pressurized casing along the entire belt conveyorl, and was fed fresh air throughout its work. It was 100 meters long, so just turning it around to excavated the second tunnel was a serious maneuver! In fact, this was done in two weeks in an unprecedented approach that even the machine’s manufacturer worried about. The exploit was well worth it – the Martina allowed the tunnel to be dug at six times the pace of traditional methods.
Besides Martina, what are the other important traits of the Bypass?
While Martina won the publicity contest due to its huge size, the Base tunnel was perhaps the real miracle. This 9-kilometer segment has sparked international interest for the innovative use of an ultra-thin and flexible ceramic lining of the tunnel, which allows for superb lighting and acoustic conditions. The Kerlite panels, made by Italy’s Panaria Group, cover 175,000 square meters; each one is only 3.5-millimeters thick but measures a meter or more on each side; apart from having the physical ability to bend with the tunnel’s internal curvatuve, they are long-lasting, fire-resistant and very cost-effective in terms of maintenance and cleaning.
All of the tunnels had to be kitted out with reversible jet fans to assure air circulation – both for health and fir ereasons. A set of axial ventilators line al the tunnels, and are themselves linked to the outside through a complex labyrinth of mini-tunnels to the sky.
It would be hard to make a last-minute change to a tunnel. Were you ever tempted?
Design work on the Valico Bypass began in 1982. These mega-projects take a long time, during which new technologies can arise, as well as financial conditions – after all, Autostrade was a state company when the project was born, but a privatized and listed joint-stock company when actual work began.
The vast scale of work, however, means that cutting corners is ill-advised. That’s a reason we relied on specialized products for all details, including fine mesh soil inserts to retain and consolidate what after all is an area whose complex clay formations are highly prone to landslides. These mesh structures serve as an erosion control blanket and allow for rapid and resilient re-vegetation, reducing the impact on the surrounding aesthetic landscape as well as serving a structural purpose.
The project is full of such details, each of which had to be incorporated into our work – allowing synchronized construction as well as a harmonious final product. The environment was always a factor. Indeed, one of the big but less-noticed gains of the Bypass, which peaks at about 250 meters below the altitude of the original highway, is that drivers will encounter much less snow, fog and low-hanging clouds, which were a big reason along with overcapacity for the relatively high accident rate of the previous main route.
We are proud to have executed such a complex project. As engineers, it is now our personal task to find satisfaction in the fact that the safe and user-friendly Valico Bypass will soon become taken for granted by millions of Italians and others who use it.