The viaducts over Zabaleta an Larrazábal streams and the Kinatoi viaduct are located on the section Elorrio – Atxondo, which is part of the HSL Vitoria – Bilbao – San Sebastián. Both structures support the double track railway of the Vitoria – Bilbao connection in the so-called Basque Y. The two viaducts have a continuous prestressed box girder deck, cast in place by means of a movable scaffolding system. Zabaleta and Larrazábal Viaduct has a total length of 566,0m, with a main span of 58,0m, whilst Kinatoi Viaduct has a main span of 65,0m and completes a total length of 880,0m. The present article describes the main characteristics of the two structures, as well as the construction sequence that was followed.
The Zabaleta and Larrazabal Streams Viaduct and the Kinatoi Viaduct are part of the Elorrio–Atxondo section of the Vitoria–Bilbao–San Sebastián High-Speed Rail Line.
Both viaducts share the same structural typology: a post-tensioned box girder constructed using a self-launching gantry. They are located in an area of remarkable natural beauty, within a valley surrounded by mountains.
The first structure, the Zabaleta and Larrazabal Streams Viaduct, has a total length of 566 metres, with a span arrangement of 30 + 42 + 50 + 58 + 50 + 5 × 58 + 46 metres, and a deck width of 14 metres (typical high-speed rail cross-section). The alignment features a variable horizontal radius, and the structural depth is 3.80 metres (L/15).
Pier heights are highly variable, ranging from 6 to 49 metres. All foundations are shallow, except for that of Abutment 2.
As its most distinctive feature, Pier 4 does not consist of a conventional shaft like the others; instead, it is a post-tensioned transverse portal frame designed to accommodate the crossing of a viaduct from the adjacent section (also designed by k2 Ingeniería and presented separately). This portal frame has a height of 49 metres and a total length of 20 metres (12 metres clear span).
The Kinatoi Stream Viaduct has a total length of 880 metres, with a span arrangement of 35 + 50 + 55 + 10 × 65 + 50 + 40 metres, and a deck width of 14 metres (typical high-speed rail cross-section). The alignment features a constant horizontal radius, and the structural depth is 4.30 metres (L/15).
Pier heights are highly variable, ranging from 12 to 72 metres, reaching considerable elevations.
The foundation typology is mixed, including shallow foundations, deep foundations with piles, and deep foundations with micropiles in one case.
Among the main constraints, the Santa Catalina Hermitage—located almost directly beneath the bridge—had to be preserved. In addition, an active landfill site in the vicinity of the structure had to be dismantled, which required suspending construction works for several months.
Both abutments follow a conventional static scheme, with one fixed abutment and the remaining supports designed as sliding bearings.
