BESIX Italy: a first bridge and the excavation of the first tunnel

In central Italy, BESIX and its Italian partner DONATI are doubling the state road 318 over 3.1 kilometers on behalf of the Italian Highway Authority ANAS. The contract includes the construction of two two-lane tunnels, a viaduct, and a bridge. At the beginning of February, one year after the start of the work, the site was marked by two remarkable milestones with the first excavations of the Casacastalda tunnel and the installation of the steel span of the Calvario bridge.

State road 318 is a crucial axis for east-west connections in Italy. Leaving Perugia, in the direction of Ancona, it passes through the beautiful hilly countryside of Umbria, including that of the Valfabbrica municipality, after which the project is named. The contract awarded by ANAS S.p.A., the company that manages the Italian public road network, includes the construction of an impressive variety of civil works, in particular the tunnels of Casacastalda and Picchiarella, which are 1,545 meters and 874 meters long respectively, the 130-metre Tre Vescovi viaduct and the 60-metre Calvario bridge. These will add two lanes of traffic to the existing road.

The Calvario Bridge...

“On 31 January, we installed the steel span of the Calvario Bridge. It is a 246-tonne steel structure, which we first assembled next to the future bridge. The operation consisted of lifting it, which we did with two 500- and 800-ton cranes, and placing it in its final position,” explains Hervé Jourquin, BESIX's deputy project manager on the site. Because of the presence of electricity poles, which required one of the cranes to be moved during the operation, the installation had to be carried out in two stages, an additional challenge that was brilliantly met by the site teams. “The next step will be to install the concrete pre-slabs and pour the reinforced concrete deck structure. From the end of March, the site machinery will be able to use it, which will facilitate traffic on site,” continues Hervé. The asphalt will not be laid until the end of the work, in two years' time.

Before the end of the year, the span of the Tre Vescovi viaduct will also be installed. The method here will be different, as the span will be pushed instead of being lifted after being assembled at one end.

...and the Casacastalda tunnel

While the span of the Calvario Bridge was being installed, a few kilometers away, the machines were preparing to start digging the Casacastalda tunnel, which is more than one and a half kilometers long. “Excavation work began on 4 February, on the eastern side. We are now preparing a second front on the other side,” explains Hervé. Theoretically, as long as the machines do not come up against large blocks of cohesive rock during the excavation, the operation should not require the use of explosives.

“We are using a traditional method, digging meter by meter and gradually installing steel beams. These form a metal ring in contact with the rock onto which concrete is sprayed,” continues Hervé. This first operation aims to secure the underground gallery in which the personnel and machines work. The final tunnel, which motorists will see, will be built in this first safety tunnel. A tube within a tube. “For the structure of the tunnel, we are using a technique called 'arco rovescio'. We make an arch on the upper part, supported by a lower arch. This requires the lower part to be poured quickly to hold the arches in the concrete,” explains Hervé. For the upper part, operations will use a rail technique to carry out the formwork, waterproofing and injection of the cap.

“We work 6 days a week, 24 hours a day. In all, with the shifts that this involves, we will have 80 people working on this tunnel, and between 120 and 150 with the Picchiarella tunnel, which will be built using the same method.” The excavation of the second tunnel is expected to start in mid-2022. In all, the two tunnels will require 8,240 tons of steel just for the consolidation of the excavation operations and a further 4,060 tons for the reinforcement.