Excavation work is now underway on the SR318 project in Italy for the new Casacastalda Tunnel, and the new Picchiarella Tunnel on the route will also be driven using the same techniques
A project in Central Italy is seeing the construction of new tunnel stretches, a bridge and a viaduct. The work is being carried out on State Road 318 by BESIX in partnership with DONATI, close to Perugia in Umbria.
The contractors are widening the route along a 3.1km highway stretch so that capacity and safety will be improved with the addition of two new lanes. The work includes building two tunnel sections, each with dual bores as well as the new bridge and new viaduct.
Excavation work is underway for the 1.5km Casacastalda Tunnel as well as for the 60m Calvario Bridge, with the steel spans being installed for the latter. Work has still to be carried out for the 874m Picchiarella Tunnel and for the 130m Tre Vescovi viaduct that also form part of the project.
“On 31st January, we installed the steel span of the Calvario Bridge. It is a 246tonne steel structure, which we first assembled next to the future bridge. The operation consisted of lifting it, which we did with two cranes, and placing it in its final position,” explained 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,” continued Hervé.
The asphalt will not be laid until the end of the work, in two years' time.
Before the end of 2022, the span of the Tre Vescovi viaduct will also be installed. The method here will be different, as the span will be pushed into place (instead of being lifted) after being assembled at one end.
Meanwhile, work is also underway to drive the bores for the nearby Casacastalda Tunnel. “Excavation work began on 4th February, on the eastern side. We are now preparing a second front on the other side,” explained Hervé. The excavation is being carried out using mechanical methods. 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 for blasting. The use of explosives for blasting work is very strictly controlled in Italy, so being able to stick to mechanical excavation only offers benefits for managing the operation as well as lowering costs.
“We are using a traditional method, digging metre by metre and gradually installing steel beams. These form a metal ring in contact with the rock onto which concrete is sprayed,” continued 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,” Hervé said. 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/week, 24 hours/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 8,240tonnes of steel just for the consolidation of the excavation operations and a further 4,060tonnes for the reinforcement.
