JOB OF THE MONTH Ӏ DECEMBER 2022


to be built required the construction of twin viaducts spanning up to 162m across the scenic Bolintxu valley to link road tunnels on each side. Apart from the large span of the


bridge, a key challenge was that the Bolintxu valley is a protected area of natural beauty and of ecological importance, so the project needed to ensure that any structure crossing it had a minimal footprint and avoided disrupting the area during installation. This meant that a conventional approach of using temporary scaffolding or support towers down in the valley could not be used.


Interbiak and structural engineering consultant Arenas&Asociados had already determined that the design of each bridge would comprise an arch spanning the valley with supports only in the form of abutments on each side. For the best way to install the arch, however, they turned to Dutch heavy lift and transport specialist Mammoet. “From the beginning we thought the


lowering method could be an effective alternative,” explained Alejandro Godoy, project manager at Arenas&Asociados. “Being aware that Mammoet was able to deliver such operations, having seen their work at the Alconetar Arches Viaduct over the Tajo River and the Bolueta Arches over the Nervion River, for the City Metro of Bilbao, they were our first call to establish the best common approach.”


LANDMARK OPERATION In order to avoid disruption to the valley, and river, below, Mammoet settled on using a swivel arch methodology, which would allow construction of the bridges by lowering an arch segment from each side of the valley. “Although this technique has been used a handful of times in recent decades, it is not common,” said Veronica Arrayago, Mammoet project manage.


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