The Olabarrie tunnel has a length of 986 m. It is a two-way tunnel with an 85 m² type section.
The excavation takes place with perforation and blasting using mechanical means, employing the backhoe, depending on the type of rock present. The tunnel cuts through lutite type materials with sandstone history. In the final part of the tunnel there is an anthropic fine ash and highly porous fill.
The support includes projected cement, pins, mesh and trusses. To complete the job, the waterproofing and coating is carried out.