The two-way Urzelai tunnel has a 95 m² type section and a length of 575 m.
This tunnel affects the cretaceous materials, both in the CLu formation (black lutites and alternation grey sandstone), as well as the Car formation (siliceous sandstone with small black lutites).
Excavation takes place using conventional methods, blasting the hardest and most abrasive rocks, and excavating using backhoes for softer and altered rock. Supports are used based on the use of productive concrete, pins, mesh and trusses. A final 30 cm waterproofed concrete formwork coating is installed.
