High Speed – Sector 2
Guipúzcoa, Spain
Conventional
Construction method
11,000 m
Excavated length
The High-Speed Rail Sector 2 project forms part of the Basque Country High-Speed Rail Network and includes more than 11 km of tunnels and underground galleries along the route between Mondragón and Bergara.
The works comprise the construction of the Karraskain and Udalaitz twin-bore tunnels, developed for single-track high-speed rail operations and designed to improve regional and national rail connectivity.
One of the main engineering challenges was excavation through the Udalaitz karst system, a highly complex geological environment that significantly influenced both the design and construction process.
Dragados carried out the excavation using the New Austrian Tunnelling Method (NATM) with drill-and-blast techniques, incorporating an intermediate access point to optimise construction progress within the Udalaitz Tunnel.
Project data
Project data
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More than 11 km of tunnels and galleries
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Udalaitz Tunnel exceeding 9 km total length (two bores)
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12 cross passages
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732,352 m³ excavation volume
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52 m² tunnel cross-section
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Excavated using NATM
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Drill-and-blast excavation
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Constructed within a complex karst system
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Intermediate access point located 3.5 km from the southern portal
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