The contract, valued at around €400m (£344m) involves the design and construction of a 17km-long undersea tunnel to extract seawater at a temperature of 2oC from a depth of around 70m in the Baltic Sea. The tunnel will be the third-longest of its type in the world, according to Acciona.
The project will use heat pumps to supply domestic hot water and heating (plus cooling during the summer months) via a district heating system across the Finnish capital.
The main tunnel is to be built using a tunnel-boring machine. The consortium will build the underground chambers to house the pumping equipment as well as the water intake caisson and pipework, as well as all the necessary engineering works. It will also build a 9km tunnel required to return excess water to the sea. This will be built by drilling and blasting.
Acciona and its consortium partner, Finnish company YIT, are working in alliance with Helen. The detailed scope of the project will be determined by the alliance during the development phase.
The development phase is expected to continue until the end of 2024 at which point the alliance hopes to move on to the implementation phase which will take about five years.
Although this is the first project of its kind for Acciona, the company has plenty of experience in conventional tunnels and TBMs, having completed more than 600km of tunnels to date. These include the longest railway tunnels in the Nordic countries (22km) in Norway and the Legacy Way tunnels in Brisbane, Australia.
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