Trans-Alpine TBM breakthrough for Caterpillar Jul 2012
TunnelTalk reporting
Excavation of the new safety and service tunnel at the Great St Bernard highway tunnel is complete after a Caterpillar (formerly Lovat) double shield hard rock TBM broke through at the end of its trans-Alpine drive.
The 5,774m tunnel, which runs parallel to the existing Great St Bernard tunnel, between Switzerland and Italy, forms the major part of safety upgrade works that began following a review of underground safety in the wake of the Mont Blanc highway tunnel fire of 1999.
Employees of Italian contractor Condotte celebrated the breakthrough at the southern (Italian) side of the safety tunnel drive alignment earlier this month (June 6). The TBM was launched from the northern (Swiss) side on October 4, 2010, achieving a monthly best advance of 640m in March this year (2012), and a daily best of 35.2m in the same month.
  • Caterpillar double shield hard rock TBM

    Caterpillar double shield hard rock TBM

  • Condotte workers celebrate breakthrough

    Condotte workers celebrate breakthrough

Average daily progress was 18m, through rock formations of mainly gneiss, schist and sandstone and under a cover of up to 950m. The tunnel is lined with a four-piece trapezoidal ring design of precast concrete segments.
The new service and safety tunnel runs parallel to the existing Great St Bernard traffic tunnel and is linked every 240m by a total of 23 individual cross passages. The main traffic tunnel, which connects Switzerland and Italy, was opened originally in 1964 as the longest road tunnel in the world. Construction of the new safety tunnel is aimed at increasing safety and improving the efficiency of technological systems and ventilation along the main tunnel.
Portal of the 5,774m safety tunnel

Portal of the 5,774m safety tunnel

tLike the Mont Blanc tunnel, between France and Italy, the Great St Bernard Tunnel, is a two lane bi-directional facility. Since being opened and to the end of 2011, nearly 26 million vehicle journeys have been made through the mountain pass. The latest safety upgrades were undertaken as a result of the Mont Blanc tunnel fire of 1999 in which 39 people lost their lives after a truck caught fire inside.
The Mont Blanc fire investigation blamed the tunnel's poor ventilation systems and inadequate refuge points for the tragedy. Drivers leaving their vehicles to seek safety were quickly overcome by toxic fumes, while those who stayed in their cars and tried to drive out became stranded when oxygen levels became insufficient to run engines.
Other safety improvements to the Great St Bernard Tunnel have included extension of the avalanche covers on the approach to the southern side.
References
Mont Blanc tunnel's 46-year history - TunnelTalk, September 2011
Fire damage rebuild of Mont Blanc road link - TunnelTalk, June 2001

           

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