Drainage Teams Go Deep Underground To Help Keep Power Flowing

National drainage contractor Lanes Group has used its specialist cutting equipment to clear pipes in a power station located in Europe’s largest man-made cavern under a Welsh mountain.

The company’s drainage engineers drove its service vehicles, including a jet vac tanker, down a tunnel into Mt Elidir Fawr to carry out the work on drainage pipes at Dinorwig hydro-electric power station.

The facility, the largest scheme of its kind in Europe, has six 300 megawatt generators that can reach full power output in just 16 seconds to meet spikes in electricity demand.

Conventional methods not effective

First Hydro Company, which operates the power station, called in Lanes to clear calcite and silt that had built up in drainage pipes located in the main inlet valve gallery, where six giant valves feed water into turbines.

Amy Pritchett, Engineering Geologist for First Hydro, said: “The calcite deposits, in particular, was beginning to compromise the gallery’s drainage system, so the work Lanes has done for us has been very important.

“Conventional methods of clearing the pipes, such as pressure washing and rodding, didn’t work, so we needed the specialist equipment and skills Lanes has to provide an effective solution.”

Minerals held in water that seeps out of the cavern’s rock walls have been deposited in channels and pipes running the 150m length of the main inlet valve gallery, greatly reducing their capacity.

Tough drainage challenges

Six enclosed clay pipes and six open channels, each up to 10 metres long and between 100mm and 150mm in diameter, had to be cleaned.
Due to the different types and durability of the minerals, Lanes has been using a range of methods to remove them so the seepage water can flow freely into a large sump.

Lanes Chester Area Development Manager Sian Wyn Jones said: “This project demonstrated the range of capabilities Lanes can bring to bear to resolve tough drainage challenges.

“The expertise, specialist equipment and determination our teams underpin the success of a tricky task. It was also a privilege for our teams to support such an awesome strategic asset that’s unique in its scale and purpose in the UK.”

Pipe descaling technology

Drainage engineers from Lanes Chester, supported by colleagues from the Lanes Sewer Renovation Division, have been carrying out the work.

To remove the deposits in the enclosed pipes, the Chester team has used a Picote Maxi Miller robotic grinder and high pressure jetting, with a specialist bulldog nozzle, designed for descaling pipes.

The Picote Maxi Miller allows an operative to remove deposits with a high degree of precision, by monitoring progress using a mini camera build into cutting head.

The Lanes sewer renovation team used an IMS robotic cutter to remove the most stubborn mineral deposits, supported by a CCTV survey team, whose HD-quality video camera also allowed progress to be monitored.

All material cut from the pipes was removed as work progressed using the jet vac tankers powerful vacuumation system so it could not escape down the pipe and risk causing further blockages.

Dinorwig – imaginative engineering

Mineral and silt deposits in the open channels were dislodged mechanically and through pressure washing, then vacuumed up to leave the area clear of debris.

Dinorwig Power Station, built in a disused slate mine in the heart of Snowdonia, was fully commissioned in 1984 and is still regarded as one of the world’s most imaginative engineering projects.

Water stored above the power station is released through the inlet valves into the turbines, and can generate electricity for five hours before the water runs out.

The turbines are then reversed to use cheap electricity to pump the water back up the mountain, ready to be used again.

When the project began in 1974, it was the largest civil engineering contract ever awarded by the UK government. Twelve million tonnes of rock were removed to create 16km of tunnel and a turbine hall 51 metres high, 180m long, and 23m wide, known as ‘the concert hall’.