This means changing the life of a city like Genoa; changing the life of a city like Milan; changing people’s lives.” So says Pietro Salini, CEO of Webuild, leader of the COCIV project consortium.
The project he is speaking of is the Terzo Valico dei Giovi rail line. It will lead north from Genoa with the intention of connecting the city more effectively with the rest of Europe. It will be 53km long, of which 36km is underground. One of the tunnels, at 27km, will be the longest rail tunnel in Italy. It is part of the Trans-European Transport Network (TEN-T), which includes roads as well as rail, and for Italy, and for Genoa in particular, it will be a vital connection.
Genoa is a major seaport and is gearing up to become bigger still: works are in progress at the Voltri and Sampierdarena terminals to allow mooring and unloading of the largest, post-Panamax container ships currently in use. But even before the collapse of its Morandi Bridge which made world headlines in August 2018, Genoa port and city were surprisingly isolated. The replacement bridge, the Genova-San Giorgio, was inaugurated in August this year, but the isolation remains.
“This will give a boost to a historic port, one with a marvellous history … but that it is surrounded by mountains, which we are excavating now,” said Salini, at a double breakthrough of TBMs on the project in September this year. Genoa does indeed have mountains all around. They cut it off and make it hard to transport goods from Genoa to other parts of Europe, so much so that many prefer shipping – sailing the extra distance around Spain and Portugal and up the Channel to Rotterdam to unload – an extra two-thousand-odd miles but still quicker and more efficient. Genoa and Rotterdam are in competition for the freight markets of the central German plain; absurdly, some of the goods unloaded at Rotterdam come back by train or truck even as far as Italy.
There are existing rail lines out of Genoa, but they are old and built to 19th-century standards, and the railhead is always congested. The northern route has a very high gradient of 3.5%, curves with tight radii, and is at saturation. The new Terzo Valico dei Giovi line will have a slope of 1.2% and much taller and wider tunnels in line with modern European standards for freight transport and rolling stock. It will provide a dedicated route connecting Genoa to Northern Italy, the Milan-Turin corridor and thence to the rest of Europe.
The trains will be high-speed and high-capacity, for goods and for people. According to Ferrovie dello Stato, the new line will be capable of carrying trucks on goods trains, a development called ‘rolling highway’, and will also carry high-cube containers, which are one foot (305mm) higher than the standard 40-foot (12.2m) shipping container.
All this is part of the investment to make the port more competitive for goods and cargo. But there is more. It will cut the journey time from Genoa to Milan from an hour and forty minutes down to approximately one hour. That is why it is so transformative for the two cities. It makes the journey between them a commute. To quote Salini, it changes “how the young live, where families send their children to school, how they pass the weekend.”
The project is part of the Rhine-Alpine Corridor, which is one of the corridors of the TEN-T strategy to connect the most densely populated and the most industrial European regions. It is also one of the busiest freight routes in Europe. And in transferring to rail a substantial share of freight traffic from trucks labouring across Europe and the Alps, it brings large savings in carbon emissions as well.
The project’s title, Terzo Valico dei Giovi, translates as Third Pass or Third Route of the Giovi. From the Bivio Fegino railway junction north of Genoa, it runs almost entirely underground, initially in the Galleria di Valico tunnel, 27km long. The Valico tunnel has four intermediate access ‘windows’ for construction and for safety. After a short stretch in the open at Libarna, the 7km Galleria Serravalle tunnel carries the alignment up to the Piana di Novi. Thereafter the line runs mainly outdoors to the 1.9-km Pozzolo tunnel, and then again in the open to join the existing Pozzolo Formigaro – Tortona line which carries the route to Milan.
The general contractor for design and construction is the Consorzio Collegamenti Integrati Veloci, or COCIV, which translates as ‘Fast Integrated Links Consortium.’ The consortium is led by Webuild, the former Salini Impregilo. The consortium has subcontracted – through international tenders – SELI Overseas to perform the TBM operations in the Serravalle tunnel. The total value of the project is some €6.2bn (US$7.3bn).
“The tunnelling alignment passes through two main geological units,” stated Aldo Mancarella and Leonardo Di Gati, respectively head of design of Terzo Valico and tunnel design manager. “The first 19.5km of the line, including most of the Valico Tunnel, runs in the Sestri Voltaggio Zone. This formation is strongly affected by the presence of ‘Argille a Palombini’, a sequence of shales and claystones with limestone lenses.
“The northern part of the Valico Tunnel, and the whole of the Serravalle Tunnel which follows it, lie in the Tertiary Piedmontese Basin which comprises a sedimentary sequence of conglomerates, marls, claystones and stiff clays.
“The hardness of encountered rocks therefore varied along the alignment. In the northern part, the Serravalle tunnels, excavation was in soil-like material, which gave, of course, no cutterhead problems.
In the Valico Tunnel, rock was generally not particularly hard, but some mediumsize boulders, having higher resistance than the rock mass, were encountered. That led to some cutterhead problems.”
The average overburden in the first (southern) 4km of the Valico Tunnel is around 100m. Thereafter, the coverage increases, reaching 420m under the Molare formation, which is where TBMs are excavating at the moment. “Here, groundwater was a consideration,” says Salvatore Caruso, director of Piemonte jobsites. “The alignment in places is 350m below groundwater level. High water pressures could occur within faults, requiring proper drainage during TBM excavation. However, hydraulic conductivity was low, meaning that water flows were also generally low or medium, so that dewatering has not been a relevant issue so far.”
All tunnels are twin-bore, with transverse connections every 500m. Six work camps have been established. Four TBMs have been used, all Herrenknecht EPB machines, of 9.77m excavation diameter, 128MN thrust force and 18MN.m nominal main drive torque and with 38 cylinders. The two Valico machines were assembled at the northern portal in a dedicated shaft 13m deep, 51m long, and 37m wide, with diaphragm walls. The two Serravalle machines were launched from a large flat worksite near the city of Novi Ligure. Navigation was by VMT and minimum radii of curvature were 1,000m. Generally, all four TBMs were operating simultaneously.
The southern section of the Valico tunnel was not excavated by TBM but conventionally. The main reason was the poor geotechnical properties of formations in the southern part of the alignments. A combination of high overburden, high tectonic stresses present in the Sestri-Voltaggio zone, and possible compressive conditions were judged too risky for TBM excavation. The southern territory was also less favorable in terms of accessibility to roads, and had smaller areas available for jobsites, depots and other areas necessary to dry TBM conditioned muck.
Instead of TBMs therefore, the ADECO-RS method, also known as the ‘New Italian’ method, was used. ADECORS (Analysis of COntrolled DEformation in Rocks and Soils) was developed in the 1980s by Pietro Lunardi and others; the intention was to develop a process which can counter the disadvantages of NATM in regard to safety and cost-effectiveness in compressive ground conditions.
While there are some similarities to NATM, the New Italian method particularly emphasises and analyses the role of the core, the section in front of the tunnel face. The properties of this region, runs the argument, are critical, as are changes in deformations and stresses within it as the face approaches it. Lunardi summarised the ADECO-RS approach as: ‘…controlling the susceptibility to deformation of the ground ahead of the face (advance core) by using appropriate stabilisation techniques’; roof bolts or reinforced shotcrete are some of those techniques.
ADECO-RS was used for the first time in 1988 on the Tasso Tunnel, and other Italian examples followed. The first application outside of Italy was in 1997 in France on the high-speed rail line between Marseille and Lyon.
“Here on the Terzo Valico we used steel ribs and shotcrete extensively to support the excavations,” says Filippo Giunta, director of the Ligurian jobsite. “In weak zones, face reinforcement was carried out using fibre-glass elements.”
A peculiar hazard of tunnelling here was the presence of asbestos. “Terzo Valico tunnels cross some formations that naturally include asbestos-containing rocks,” says Francesco Poma, construction coordinator. “This is the case, for example, with serpentines, metagabbros and metabasalts. Given this geological context, investigations of the likelihood of asbestos were carried out from the preliminary design stage, which allowed us to define the main risks along the alignment.
“Excavations up to now (November 2020) have shown that these rocks were more often encountered in the northern (Piedmonte) part of the alignment than on the Ligurian side, where occurrence was more isolated. We have found mostly Chrysotile (white asbestos), and sometimes Actinolite and Tremolite.” (Both minerals, when in fibrous form, are classed as types of asbestos). “We have never found Crocidolite (blue asbestos).” Because of its straight, needle-like fibres, blue asbestos is thought to be the most hazardous of the asbestos minerals; the other types generally have curlier fibres that are inhaled less easily.
“We adopted strict precautions in asbestos-containing contexts. A specific protocol for the management of asbestos risks was developed, working with the Osservatorio Ambientale del Terzo Valico to do so. Procedures and work organisation were adopted, along with special systems and installations” (see box, opposite page). “At certain jobsites, for example at the Pozzo Radimero site, the adaptations took time to implement and caused some delays.
“Tunnels were lined with universal ring segments in a six plus one arrangement, with EPDM gaskets around the perimeters. Small quantities of polymer fibres were added to the mix. The segments are 1.8m wide and 400mm thick. They are produced in three different plants in Northern Italy, transported by truck to the portals and then by multiservice vehicle to the TBMs. We used a longitudinal connection system to increase the shear strength between each ring and the previous one” says Salvatore Caruso.
The entire project produced around 14,000,000m3 of muck and excavated material, 2,500,000m3 of which was from the TBMs. About 15% was re-used on the project; the remainder was used to restore used quarry sites. “The muck contained additives that had been used for ground conditioning ahead of the TBMs” said Giovanni Parisi, director of construction.
“This needed particular attention before the muck could be re-used. A specific ecotoxicity study was carried out, to define for each additive used within the TBM excavation a certain reference threshold concentration not to be exceeded. In practice, the excavated material was dumped on the ground in layers, which allows both drying and the natural biodegradation of the additives to concentrations below those thresholds.
For that purpose, a specific area has been designated as an intermediate muck depot; it can manage material coming from all four TBMs at the same time – about 10,000 tonnes of it every day.”
On 24 September 2020, breakthroughs came simultaneously on one of the Serravalle tunnels, and in a northern stretch of the Valico Tunnel. Completion of the new line is scheduled for the end of 2024.
