Armand van Wijck, TunnelTalk Europe correspondent
After a long and uncertain period, due to the Euro Zone economic crisis, project protests and political issues, the much debated Mont d'Ambin rail tunnel might finally see a ground-breaking within two years. TunnelTalk Europe correspondent Armand van Wijck examined the multi-billion mega project and talked with Project Leader Maurizio Bufalini.
- Eight TBMs of various design plus open face excavation is the plan of attack for excavation of the Mont d'Ambin base railway tunnel on the new high-speed link between Lyon and Turin. Working from both portals and in both directions from three of the four intermediate access adits, construction of the 57km long twin tube tunnel is expected to take 10 years.
Figs 1 and 2. Plan (left) and section of the new east-west Alpine base tunnel between France and Italy and well below the existing Fréjus tunnel elevation (right) - gradient figures are in permille (‰), move decimal point one place to the left for percent (%)
- With the majority of the funding in place and the remaining 40% covered by an application to the European Commission, development of the construction procurement contracts is on a schedule that would see excavation of the main baseline tubes begin in 2015.
Fig 3. Construction of the base tunnel includes excavation of four intermediate adits
- "We have completed drill+blast excavation of three of the four access adits and the fourth, in Italy, has just begun," said Maurizio Bufalini, leader of the project in an exclusive interview with TunnelTalk. "Our next milestone is to introduce the first TBM on the project at the La Maddelena Adit. This is expected within two months, about October 2013, and will provide valuable information about how the TBMs will perform in the anticipated rock conditions."
- At 57km-long, the Mont d'Ambin alpine base tunnel is a vital part of what is to become the 270km Lyon-Turin high-speed rail link. It lies at the heart of the trans-European rail network, on the border between France and Italy, connecting east and west Europe. The rail link made it onto the European Commission list of 14 priority projects in 1994. When finished it will share the title of longest European rail tunnel with the Gotthard base tunnel in Switzerland.
|Table 1. Key dates in development of the international rail link|
|1991 November||Convention of Salzburg, which aimed at reducing the environmental impact and risks in intra - and trans-alpine transport. First suggestion of Mont d'Ambin base tunnel.|
|1994 December||Lyon-Turin rail link made a priority project by the European Commission|
|2001 January||Signing of the Franco-Italian Inter governmental agreement for the construction|
|2001 October||Foundation of LTF|
|2002 April||Excavation starts on first access tunnel at Modane|
|2003 March||Beginning of work at Saint-Martin-la-Porte|
|2005 October||Beginning of work at La Praz|
|2012 January||Signing of the Franco-Italian Inter governmental agreement on base tunnel funding|
|2012 November||Start of survey gallery excavation at La Maddalena|
|2015 Summer||Possible start of base tunnel construction|
|2025||Possible delivery of base tunnel civil works|
- Lyon-Turin Ferroviaire (LTF), a joint subsidiary of Réseau Ferré de France (RFF) and Rete Ferroviaria Italiana (RFI), is project owner and promoter of the international link since its establishment in 2001 and with Maurizio Bufalini appointed as its Project Leader. According to LTF, there are several major advantages and benefits of the new line. Principal among these include increased safety - as offered by rail transportation in comparison to road - as well as the reduction of road traffic, noise pollution and CO2 emissions.
- It will have cross passages every 333m, to correspond with the length of a double deck TGV passenger train, and three safety stations located along the survey galleries excavated from the intermediate adits (Fig 4). Four access tunnels will be available during construction with lengths varying from 2,400m to 7,541m. The three located in France were excavated by drill+blast and are already completed. "Right now we are finally working on the Italian one," said Bufalini. "We are at 200m today (July 2013) and in two months we will excavate further with a TBM. This last access tunnel at 7.5km long, should be finished in about two years."
La Maddalena access portal with the Alpine highway running above
- Next year LTF will prepare the tenders for the construction of the base tunnel. "Italy and France still need to agree on the exact tender packages," said Bufalini, "but it will be no more than six lots for the civil works. We need at least one year for this process. Afterwards the construction works can begin. That will be about three years from now." According to Bufalini it will take about 10 years to construct the base tunnel.
- To date, the project has cost about €842 million and for work completed between 2001 and 2011. In total, the base tunnel is expected to cost €8.8 billion in January 2012 figures. "We are currently making preparations to ask the European Union for 40% of the funding," said Bufalini. In January 2012, Italy and France agreed on the funding for the remaining 60% of the money. Italy will pay 57.9% and France 42.1% percent. Both countries have an equal responsibility for construction of the project.
Establishment of the La Maddalena access portal
Squeezing coal schists
The excavation of the access and survey tunnels proved valuable for analysing potential geological conditions along the main route alignment. The greatest challenge was the squeezing and time-dependent behaviour of the coal-bearing schists of the Saint-Martin-la-Porte access tunnel, with very high convergences of often more than one meter. This will also prove a challenge during base tunnel construction in that section.
- "This imposed the study of a three phased excavation method," explained Bufalini. "First, advancement with deformable support to permit convergence. Then reaming to the original diameter of the tunnel, and lastly, cast in-situ concrete lining to definitely stop the deformations."
- The next challenge will be the 6m diameter hard rock TBM that will soon start excavating the Maddalena survey gallery. "This will function as a 1:2 scale test of the future 10,5m diameter TBMs of the main base tunnel tubes. We are to expect high overburden conditions of more than 2,000m, with associated rockburst phenomena and high rock and groundwater temperatures of up to 45°C."
- The access tunnels will be used to excavate the base tunnel on several fronts simultaneously. Together with sections of drill+blast, eight TBMs are planned for the job. Two dual-mode slurry shields, two mixed-ground shields and four hard rock TBMs for high overburden sections. Shield diameters will vary between 6m for certain access tunnels and 10.5m for the base tunnel.
TBM excavation will complete the La Maddalena access adit from the concrete lined drill+blast starter tunnel
- The base tunnel will be excavated from the two portals St Jean de Maurienne in France and Susa in Italy and from the three intermediate access tunnels in France, for a total of 16 advancement faces. The longest section will be a 19km TBM drive heading east towards Italy from the Modane access tunnel (Fig 4). As well as a majority of the excavation by TBM, drill+blast will also be used for certain sections including reaches between Saint-Martin-la-Porte and La Praz to where open face excavation will deal more effectively with the squeezing and time-dependent behavior of the coal-bearing schists. LTF has prepared one tender for what it states is the most difficult part of the project. "The contract is for the construction of a survey gallery on the main tunnel alignment from Saint-Martin-la-Porte to La Praz. During excavation of the access tunnel, a section with a diameter of 10m, deformation of up to 2m in diameter was observed over a period of a few days. It is impossible to use a TBM in that kind of situation. Those reaches require excavation traditional open-face methods."
- This is the first article of a three-part series on the Mont d'Ambin rail tunnel. The next one will discuss the safety aspects of the base tunnel into operation.
Extreme tunnel planned for Andes rail link - TunnelTalk, November 2012
Final finish for Gotthard Baseline excavation - TunnelTalk, March 2011
Brenner project takes a major leap forward - TunnelTalk, February 2011
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