tunnel is located between the km 621 + 192 and 621 + 318.1, with a total length of
126.10 meters. “El Arroyo”
tunnel is located between the km 622 + 037.5 and 622 + 260.8, with a total length of 223.30m
. Both tunnels are located on the Karrantza-Aranguren route, belonging to the 780 Bilbao Concordia-Santander metre-gauge line, in Zalla, in the province of Biscay, and have a lining formed by masonry on the gables and brick in the vault.
Due to the conditions of the tunnels and the need to electrify the line, it was necessary to reinforce and widen the gauge, first raising the track to be able to work with conventional machinery. The works that were carried out were the following:
- Placement of existing cladding support structure (temporary trusses).
- Demolition of the lining and mechanized excavation of the land.
- Debris removal and cleaning of the land.
- Sealing of the land with shotcrete reinforced with metallic fibers.
- Placement of the support elements according to the needs of the excavated land according to the defined support sections.
- Final lining with shotcrete reinforced with polypropylene fibers for fire resistance.