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La Praz site

TBM Federica in La Praz
TBM Federica in La Praz


With a length of 2,800 m and a 12% down gradient, the access adit of La Praz is located on the right bank of the River Arc and is divided into two sections, the second being parallel with the future base tunnel.



The La Praz access adit is located in the municipality of Saint’André, and was tunneled using a traditional technique (explosives) between 2005 and 2009 involving about 110 direct workers, 49% of whom were from the Rhône-Alpes region. Once the base tunnel becomes operational, the access adit will serve as a ventilation duct, and as a maintenance and safety passage.

Management of water seepage

In geological terms, the data collected reveals excellent rock reliability. The hydrological conditions included underground aquifers in the first 500 metres of excavation which had to be managed by testing the most appropriate solution in order to limit interference with surface water resources. As a result, resin was injected inside the tunnel in order to reduce water seepage and guarantee reduced permeability in the tunnel.

Data key

2.700 m of length

2005-2009: duration of the worksite

12% slope

110 direct workers

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