The AP-8, known as Supersur, is the Bilbao ring road. In its last section it crosses a particularly complex orography area that has led to the construction of the 1950 m long Arnotegi tunnels and the 620m long Seberetxe tunnels. The connection between these two works is carried out by saving the Bolintxu ravine, an enclave of high scenic interest and whose environmental characteristics with rich native flora should be protected. To meet these strict design and construction requirements, an innovative solution of great technical complexity was chosen that respects the natural conditions of the valley.
The Bolintxu arches are two viaducts, one for each axis of the AP-8 route, with a double lower arch that bridge a span between abutments of 162m (axis 1) and 142m (axis 2).
The composite section arches, with a metal box filled with concrete, have a variable depth between 2.20 m and 1.50 m. The transverse bracing between each pair of arches, spaced 5,40 m apart, is carried out by means of diagonals 0.3 m wide and 15 mm thick.
The composite deck is made up of two metal box girders 1.20 m wide and 0.85 m deep separated by 5.40 m with transverse ribs placed every 3.33 m that allow the deck to reach 14 m wide and serve two lanes of 3.50 m, two shoulders of 1 and 2.50 m and two sidewalks of 1 and 2.50 m.
The arches are built by lowering method, reaching the construction site through the tunnels that they connect, thus guaranteeing the non-alteration of the Bolintxu natural space. Noise protection barriers and a detailed landscape restoration plan to integrate the abutments will help to protect the valley in the exploitation phase.
