of tunnel

Construction of more than 12.6 kilometers of tunnel with a diameter of 2.9 meters.

ACCIONA, in collaboration with Sacyr, carried out the construction of the Mularroya dam transfer tunnel in Zaragoza. This project included the design and construction of the dam, the diversion dam and the diversion pipeline, including the construction of more than 12.6 kilometers of tunnel with a diameter of 2.9 meters.

More than 8,200 meters were excavated to the tunnel’s halfway point, using a tunnel boring machine that had been modified to adapt to the specific geological conditions of the route. This section of the tunnel runs along the bottom of an open valley for 80 meters, where the new entrance portal is located.

The tunnel boring machine used on the project, originally a double-shield TBM, was adapted to the specific needs of this project and a single-shield rock TBM was chosen due to the complex geology of the route.


In line with its commitment to sustainability, the joint venture (UTE) implemented measures such as the use of conveyor belts for the removal of earth, minimizing the use of locomotives, which are also electric.

This choice contributes to reducing to zero the emissions of polluting gases generated by transportation inside the tunnel during its construction, in line with ACCIONA's sustainability principles.


  • Location: Zaragoza, Spain.
  • Contract type:
  • Infrastructure: +12.6 km of tunnel with a diameter of 2.9 meters.
  • Year of completion:

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