The underwater Lamiako tunnel project in Bilbao estuary

The underwater Lamiako Tunnel project, promoted by Biscay Territorial Council (Bilbao, Spain) and currently in an advanced study phase, defines the 4,5 km long road link between the riverbanks of Bilbao estuary. It comprises the two twin-tube tunnel section of 3,5 km and a grade separated junction at each end: Ballonti junction at the left bank, and Artaza junction in a densely populated zone at the right. It will connect the high capacity roads along both riverbanks of the west side of Bilbao Metropolitan area, which at present has only one road connection along the 14 km of the estuary downstream from Bilbao, i.e., Rontegi Bridge. This fact entails four problems in the road network of the area: recurrent congestion, excessive trip distances and time, lack of connections or alternative routes, and vulnerability to accidents and natural hazards. Lamiako Tunnel will close the high capacity roads loop west of Rontegi, in order to solve the mentioned problems. The tunnel will be bored in rock. Ballonti open-air junction is formed by several bridges. Artaza junction, consisting of 6 road branches along more than 2 km, completely underground, thus reducing social and environmental impacts, will be built with diaphragm walls and jet grouting. The project study has required geological, hydrogeological and geotechnical dense field campaign and studies, thorough geometric layout studies and traffic analyses and modelling, and geomechanical and structural design and analysis. Moreover, it is under study the option of partially sharing the road link with a metro-type section, giving thus rise to a multimodal tunnel. The costs of the works are approximately 450 million euro, for which recently the European Investment Bank has granted a 200 million euro loan to the Biscay Council. Features of the project study have permitted to draw several concepts which may contribute to establish a methodology for studies of this type of infrastructures in similar scenarios.