Tunnel 11 has a mine length of 412 m with an excavation section of some 104 m².
Excavation has taken place along the terrace with thickness that exceeds 90 m, with mechanical means, using a backhoe with hydraulic hammer.
The designed support consisted in:
12 m length openings with 80.9 mm diameter exterior micropile, that are 7 mm thick, overlapped at 3 m. Rock bolts, injected with cement, 4 m in length, with a 1 m x 1 m spacing. 150Mmx150mmx6mm electro-welded mesh.15 cm thick layer of shotcrete around the excavation and HEB 100 metallic trusses. 20 cm thick concrete and HEB 160 crosses were installed in the tunnel entrance.
Metallic arches on the upper section when required, and the construction of a temporary slab during excavation of the upper section.
Bolts were also necessary in the drainage perforations for key reinforcement and drainage of the forepart of the excavation.
