Strabag completes 1.2km exploratory tunnel for Coire Glas pumped hydro storage scheme

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A multi-disciplinary team of more than 100 people has been working at a fully operational tunnel construction site on the banks of Loch Lochy, a remote location 32km from Fort William, since December 2022.

They used a drill and blast technique, rarely used in the UK, to adapt to the variations in rock type and the geological conditions on site.

The exploratory works are at the site of the proposed Coire Glas large-scale pumped storage hydroelectric project for SSE Renewables.

With a potential capacity of up to 1,500MW and energy storage of around 30GWh, the scheme would double the UK’s existing electricity storage capacity, providing homegrown renewable energy when the demand is high or if other variable generation decreases.

The exploratory works involved the creation of a tunnel approximately 4.5m wide, cutting into the hillside towards the proposed location of the underground powerhouse complex, followed by ground investigation.

The purpose of the tunnel is to acquire information on the geological conditions of the proposed location to inform the detailed design of the main works.

The drill and blast technique sees holes drilled into the rock followed by blasting, where the holes are filled with explosives and detonated in a controlled manner. The blast fractures the rock, facilitating its removal and allowing for the tunnel to progress.

Work took place in compounds surrounded by nearby forest, a steep hillside, and the shoreline of Loch Lochy, meaning Strabag had to work collaboratively with Scottish Environment Protection Agency to monitor tunnel effluent and noise emissions, to minimise their impact.

The team worked in shifts across 24 hours, seven days per week.

Last year NCE spoke to SSE and designer Cowi to find out more about the challenges of the project.

Strabag UK managing director Simon Wild said: “To set up a fully operational tunnel construction site from scratch with all the necessary infrastructure in such a remote location has been a huge achievement for our team.

“Our use of the drill and blast technique in particular demonstrates our industry-leading expertise.”

SSE Renewables director of development at Coire Glas Mike Seaton added: “Completing the tunnelling is testament to the hard work and dedication of everyone involved and a positive step forward in de-risking the project.

“The works progressed to plan, and samples of the materials excavated from within the hillside are currently being analysed. The findings of the tunnelling works will be used to inform the final design, including the detailed design of underground structures, and will be a key consideration in any final decisions related to the project.”

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