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Tunnelling leads on Italy’s Terzo Valico rail link 11 Aug 2016

Patrick Reynolds for TunnelTalk

The Terzo Valico high speed rail link is currently the largest tunnelling and infrastructure project in Italy. The venture forms the southern part of an EU-backed strategic transport corridor and cuts twin tube tunnels through complex geology along more than 34km of the 54km project distance between Milan and Genoa. The Valico Tunnel in the south is approximately 27km pairs with the Serravalle Tunnel in the north at more than 7km long. Conventional excavation is underway on the Valico Tunnel with TBM headings preparing to begin in 2017 and about to launch on the Serravalle Tunnel. Main project contractor, the Salini Impregilo led JV with Condotte and Civ has subcontracted Seli Overseas to complete the Serravalle Tunnel TBM operations.

Figs 1a (top), 1b (left), 1c: More than 34km of the 54km long Terzo Valico Milan-Genoa high speed rail link is aligned underground

The Terzo Valico high speed rail project in Italy is at the south end of a EU priority transport upgrade of the Rhine-Alpine rail corridor that extends between Genoa and Rotterdam via Switzerland and Germany (Fig 1). The project is being developed by Italian rail network company RFI SpA as a mostly underground alignment of twin tube tunnels at about 35m apart and linked with cross passages at 500m intervals.

Planning for the project began about 12 years ago, and in 2006 the design concept was approved. In November 2011, the all-Italian Consorzio Collegamenti Integrati Veloci (COCIV) led by Salini Impregilo and including Condotte and Civ was awarded the turnkey contract to fully deliver maximum design rail speed of 250km/hr Terzo Valico, including all civil and M&E works and detailed engineering. With a total value of approximately €4.5 billion, the contract is under supervision by ITALFERR and is scheduled for completion in 2021.

Construction is arranged in six packages with excavation of two long tunnels taking more than 34km of the total 54km long connection through TBM and conventional open-face tunnels to maintain high speed rail services.

To the south the link, the Valico Tunnel, at 27.1km long, takes the rail line almost as far south as Genoa, linking into the southern rail network via the conventional open faced Campasso Tunnel completed by COCIV in July 2015 and new interconnection tunnels of about 2km each to Voltri (Fig 1b).

First mainline TBM assembly on Terzo Valico rail project
First mainline TBM assembly on Terzo Valico rail project

To the north and separated by a short surface section between portals is the shorter 7.1km long Serravalle twin tube tunnel.

The strategy of the main contractor is to subcontract execution of the main line TBM excavations and is completing the open-face conventional headings itself. Seli Overseas is signed as TBM subcontractor on the Serravalle Lot, and it is on this section where the first of four TBMs procured for the project will launch in the coming weeks.

TunnelTalk met COCIV General Manager Ettore Pagani at the 2016 Swiss Tunnel Congress who explained that procurement plans are in preparation for a second TBM excavation subcontract for the 9km long northern portion of the long Valico Tunnel where the second pair of TBMs will be launched in 2017. For the 18km southern section of the Valico Tunnel, the contractor is using conventional open-face tunnelling methods on several headings opened up from a number of intermediate adits.

9.73m cutterhead for  the first Serravalle Tunnel EPBM
9.73m cutterhead for the first Serravalle Tunnel EPBM

Addressing the recent Swiss Tunnel Congress, Pagani reported that at the end of May, the project had completed a total of about 7.5km of tunnel excavation including starter tunnels at the portals, completion of the Campasso Tunnel, and excavation of two of the Valico tunnel adits at Vallemme and Polcevera.

By 2017, with conventional open face tunnelling under way on the main tunnel headings in the south, and all four TBMs in operation in the north, a total of 10 headings will be under excavation, said Pagani. These operations will be supported by seven base camps and 17 construction sites along the whole length of the project.

The four TBMs for the main tunnel bores were ordered from Herrenknecht AG following earlier use by COCIV of a Herrenknecht machine to bore the 1,958m long intermediate adit at Polcevera for the long Valico Tunnel. All are EPBMs and the first two of the four will launch before the end of 2016 by Seli Overseas to complete the 6.3km drives for the 7.1km long Serravalle Tunnel.

Breakthrough by COCIV in 2015 of the Campasso Tunnel
Breakthrough by COCIV in 2015 of the Campasso Tunnel

The first of the two 9.73m diameter EPBMs for the Serravalle Tunnel is under assembly ahead of a launch in September/October (2016).

Geology along the twin tunnel alignment comprises mostly clays, sandstones, marls and conglomerate. The EPBMs will be launched under a low overburden from the north portal and will install a 400mm thick precast concrete segmental lining 1.8m wide rings of six segments and a key as they progress.

Excavation of the Valico Tunnel involves tunnelling through more complex geology. “The tunnel is only half as long as the Gotthard high speed rail base tunnel but it will be challenging to build,” explained Pagani. “Almost a third of the alignment traverses the Sestril Voltaggio Zone under an overburden of up to 600m and through a long fault zone.

Excavtion and lining work of the Vallemme adit
Excavation and lining works on the Castagnola adit

When speaking to TunnelTalk, Pagani said that the geology of the northern and southern sections of the long Valico Tunnel are distinctly different. “Rock towards the north is similar to conditions on the Serravalle alignment,” he said “comprising sandstones and marls but with an expectation of medium to high fracturing. Most of the rest of the tunnel to the south, conditions consist of schists, hydrogeological features, occasional limestones with notable fracturing and the anticipation of high deformations.”

The southern portion also features the geological complication of localised deposits of asbestos in the face of one of the adits.

For the 9km long northern portion of the Valico Tunnel, COCIV has selected a pair of 9.77m diameter Herrenknecht EPBMs machines that are to launch in 2017.

Early face work in the Crevasco adit
Early face work in the Crevasco adit

Ahead of that COCIV is performing a total 6km of adit construction and advancing the 18,000m southern section of conventional open-faced mined tunnels for the Valico Tunnel.

Initial works have focused on excavation of the four adits in preparation for opening up the main tunnels. These are located, from the north, Vallemme (962m), Castagnola (1,782m), Cravasco (1,260m), and at Polcevera (1,958m long).

In July 2015 the JV completed the first, relatively short, section of main tunnel – the Campasso Tunnel at the southern end of the Valico Tunnel. This alignment takes the main running tunnels off and into a single tube, twin track tunnel for linking with local rail networks.

Excavation of the 1,260m-long Cravasco adit has been unexpectedly challenging due to particular difficulties in dealing with naturally occurring asbestos. The asbestos zone was encountered earlier this year (2016) along a stretch of approximately 100m starting at about 700m into the heading. The contractor is operating a three-zone (A-C) isolation and handling system to deal with the excavated asbestos, starting with sliding doors and waterproofing material, to prevent contamination as the fibres are removed for processing. The asbestos is handled as hazardous waste and is being stored as such until final disposal, explained Pagani.

Lining of the TBM bored Polcevera adit (left) and lining of the adit’s working chamber

With work well underway excavation of the main tunnels from the total of 10 headings will progress towards TBM and open-face breakthroughs and towards an opening of the new line in 2021.

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