Plan of attack for Lyon-Turin base railway contracts

Plan of attack for Lyon-Turin contracts in France 16 Jul 2021 TunnelTalk reporting Following award of the three main excavation contracts in France for construction of the Mount Cenis baseline railway through the Alps on the Lyon-Turin link, the client TELT provides further information about their plan of attack.

With a total construction value of more than €3 billion and with construction insurance for each provided by TELT, the three contracts are let to the selected consortia on a design-build basis (Table 1). Detailed design will progress through the coming months and excavation is expected to begin in Summer 2022. Of the total 97km of excavation covered by the three contracts, 54km will be by five TBMs and the remaining 43km will be by drill+blast and conventional openface methods for the main tubes of Lot 3 and the the cross passages, caverns, underground adits, loop lines and ancillary excavations on Lots 1, 2 and 3 (Fig 1).

Fig 1. Main construction lots for the 57.3km long twin tube Mount Cenis railway on the new Lyon-Turin trans Alps line Of the five TBMs to be applied, three are shield machines to erect a specified precast segmental lining for the three Lot 2 drives, and two are open gripper rock TBMs for the twin 15.2km long drives on Lot 1.The rock TBM drives and the conventional excavation headings will be finished with a secondary in-situ concrete lining.

Geological conditions to be anticipated along the 57.5km twin tube railway alignment, with 12.5 km in Italy and 45km in France, are based on the reference geological modelling data obtained during completed excavation works. These include the Saint- Martin-La-Porte, La Praz and Modane inclined access adits in France, the La Madallena access adit and exploratory rock TBM drive in Italy, and the 11.25m diameter segmentally lined TBM main south running tunnel drive from the Saint-Martin-la Porte adit to the La Praz adit and a 1.4km section of the same south tube excavated using conventional methods through a reach of poor geological conditions. These data indicate that the greatest geological risks to the excavations beneath a maximum mountain overburden of 2,200m will be water ingress, squeezing and time-dependent behaviour, abrasivity, fault zones, rockbursting, geothermal high temperatures, methane gas and karstic voids.

Pre-excavation grouting is part of the construction contracts for water ingress control and ground stability for both TBM drives and the conventional excavation headings. Systematic probing is also a requirement. Fiberglass and self-drilling anchor bolts are used to stabilise the face of conventional excavations with rock bolts, arches and shotcrete providing primary support and lining. Full round waterproofing systems to withstand up to 10 bar hydrostatic pressure will be applied behind

cast in-situ final linings with pre-excavation grouting and gaskets providing long term water control of the TBM segmentally lined headings. According to TELT, expected drainage water at the portals of the completed project is to be exploited for drinking water and local district heating systems.

In addition to a focus on environmental protection and the application of BIM for data recording, TELT has made the reduction of waste another project priority. As an example, about 60% of the excavated rock is to be recycled and used as aggregate for fabrication of segments and for railway embankments on the surface sections of the line. The higher the percentage of reused rock, said TELT, the fewer natural resources will be needed, which in turn eliminates the transportation of materials from quarries to the construction sites.

Where other long distance rail projects, including the Eurotunnel undersea link between the UK and France and the current Brenner baseline railway between Austria and Italy, have included a central advanced service, safety, exploratory and long term drainage tunnel, the decision not to include a central service tunnel on the Mount Cenis link has been made, according to TELT, “to optimise the excavation and operation phases with lower costs and the same benefits. In particular, exploratory studies were carried out through the excavation of the intermediate access adits and the first 9km of TBM excavation on the axis of the future running tunnel between Saint-Martin-laPorte and La Praz.

“For railway safety during operation and in compliance with the current technical specifications for interoperability, the project foresees three underground safety areas at La Praz, Modane, and Clarea, with a maximum distance of 20km between them. These safety areas provide a secure reception room between the two railway tubes and a highcapacity suction ventilation system to manage smoke throughout the tunnel if or when needed. Cross passages at 333m intervals provide rapid access to the other tube as the ultimate safe place in the event an emergency situation train cannot reach one of the safety areas. There are also compartmentalised and self-extinguishing technical rooms in the underground alignment.”

When completed and in service, the new Lyon-Turin baseline railway will provide greater freight capacity with freight trains of up to 1,500 tonne passing through, compared to the current 600-700 tonne trains. When operational, up to 256 freight trains/day are expected on the line, comprising 18 Modalohr trains, 80 large-gauge rail motorway trains, and 158 freight trains. This traffic is estimated to eliminate 60 heavy goods vehicles/day travelling on the cross border Alpine road networks. For passengers, 22 passenger trains/day are expected with eight additional trains/day during the winter skiing season in the Italian and French mountains. Express trains from Lyon to Turin will take 1hr 47min, against the current 3hr 47min with Milan-Paris journeys reduced from 7hr to 4.5hrs. More connections for departures from and destinations to other European cities on different European routes will encourage new passengers to train travel. [] References Main works awards for Lyon-Turin base rail line – TunnelTalk, July 2021

TBM and conventional excavation to be applied

Current excavation to create TBM assembly caverns

Earlier adit excavations provided geological exploration

Excavated rock will be recycled into segment production