Acciona and its partner, Sacyr, have made the final breakthrough on the Mularroya dam transfer tunnel in Spain. Zaragoza

Acciona’s UTE carried out the project, which includes the design and construction of the Mularroya dam, including 13.3km tunnel, with a diameter of nearly 3m, as well as the construction of the diversion pipeline and a national road bypass.

Construction of the tunnel near the city of Zaragoza began in 2020 and, by the end of 2022, more than 8.2km had been excavated. From there, work continued on an open route before excavation of the last 5km of tunnel began at the start of 2023

Before the TBM was launched, 61m of conventional excavation was completed using forepoling minipiles, TH-21 steel ribs, and shotcrete.

For the excavation, a Herrenknecht double-shield TBM was refurbished to provide the single-shield rock TBM required for the complex geology of the route. To service the the tunnel’s long length and limited internal diameter a conveyor belt was used to remove the spoil, minimising the use of electric locomotives. Acciona says this resulted in zero emissions from the transport used inside the tunnel during execution.

Typsa, which was responsible for the construction control and supervision, says the Mularroya tunnel is “one of the most unique hydraulic works carried out in Spain in recent decades, and a reference for hydraulic tunnels under construction in Europe”.