TBM link to Messina Strait cable crossing
Sep 2011
SELI News Release
- High-voltage cables will travel an underground route before making a cable crossing of the Messina Strait from Sicily to the Italian mainland. Two sets of 380kW cable from the Scilla power station, about 630m above sea level on Sicily, will connect from the Favazzina marine harbor via cable laying on the sea bed to a power station in Calabria (Fig 1).
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Fig 1. Cable crossing of the Messina Strait
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Fig 2. Underground works plan
- SELI is awarded a €38 million contract by TERNA, the electricity power transmission company, to complete the underground works (Fig 2). The 2,842m long tunnel, worth €17 million of the contract, will be excavated using a 4.09m diameter double shield TBM. Working on a constant 10% incline, the tunnel connects to a 353m deep x 7m diameter shaft and to the Scilla power station. En route the bored tunnel passes under the alignment of a planned twin-tube highway tunnel, as well as under an existing twin-tube road tunnel and beneath a gas pipeline gallery.
- The geology, in this seismically active part of the world, includes several fault zones (Fig 3). The TBM to be used for the project will have several new features.
- The 4.09m diameter cutterhead will be dressed with 27 x 17in cutters; numbers 1 to 14 are face cutters, 15 to 26 are peripheral, and cutter 27 is an overcutter to add 5cm to the cut diameter. The cutterhead will be powered by five 200kW electric motors for a total output of 1,000kW and optimum speed of the cutterhead, able to rotate in either direction, will be between 10 and 11 rev/min, with a maximum speed of 14 rev/min.
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Fig 3. The geology includes several fault zones
- The main drive system will have a thrust of 12,000kN through 8 cylinders. The eight rear auxiliary thrust rams will provide for a maximum thrust of 16,125kN. The gripper system will have a total of 4,310kN for the two hydraulic cylinders.
- A 500mm wide continuous conveyor will haul muck at a speed of 2.5m/sec and a maximum capacity of 250 tonne/h.
- A diesel climber will be used in the rail handling system. Locomotives with friction rather than rubber wheels are now an established technique to overcome slopes greater than 10% and ensure a greater degree of safety. A hydraulic system, powered by a 300kW diesel engine, will take the convoy through the traction unit (Vulkolan coated wheels that will run on the monorail station attached at a default height).
- Excavation is scheduled to begin in May 2012 and to be completed in March 2014.
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