Completed in 1934, the St Germans pumping station had originally been earmarked for upgrading and refurbishment in 2010. Following further evaluation, however, it became apparent that the building would not be viable due to the high cost of servicing the 64-year old pumps.
The Middle Level Commissioners took the decision to demolish the original building, including the two metre thick concrete slipways and sluice gates that were more than a metre under water to make way for a new £40 million pumping station.
The pumping station is a vital part of the water control on the Great River Ouse, and marks the high water point in the tidal reach of the river. The site houses the largest pumping station in the country, and keeps the river levels under control on 700 km2 of the Fens, south of Kings Lynn. Offering protection to 24,000 homes, 1,100 commercial properties and 70,000 hectares of high grade agricultural land in the area, the new station has six state-of-the-art pumps capable of moving 100 m3 of water per second, and on one test to lower the levels, they pumped 150,000,000 litres of water during a single morning.
As part of the upgrading process, main contractor Costain had used another demolition contractor to demolish the upper building structure.
But a specialist demolition contractor was required to undertake the underwater work, in particular the operation of hydraulic breakers underwater; and that is where GBM Demolition came in. The Lincolnshire-based company is using a Caterpillar 345 excavator mounted on a 60 tonne floating pontoon to remove the outer weed screen.
The excavator with a 20 metre long reach boom and equipped with an electronic dig system that places the bucket accurately by a remote sensor enabling it to efficiently work under water to remove the underwater structures. A Volvo EC700 and a Komatsu PC450, both fitted with Sandvik BR4511 3,800kg breakers supplied by Sandvik’s dealer for North East Midlands AMS Bobcat Ltd, are working under water breaking reinforced concrete at the side of the sluiceways, with the Komatsu PC450 wading into the lagoon to demolish the slipways.
"It was impossible to dam the water supply so we were forced to provide a demolition solution that would work under water. Working under water with a breaker presents all sorts of problems,” explains contracts manager Mark Kime.
"We are using special grease for the breakers and all the hydraulic oil has to be bio-degradable for a start. But the biggest problem is ensuring that water does not enter the hydraulic system through the breaker. This can only be done by operating the breaker with a constant 5 bar pneumatic air supply supplied by mobile compressors, and connected to an air input point designed for underwater applications. But there is always the risk that if the air supply fails, then water will enter the system within seconds and destroy the hydraulics. Sandvik have installed safety cut-off systems for the breakers that sound warnings and isolate the breakers long before any damage could be done. It is a system that clearly works, and allows GBM Demolition to operate the breakers under water with confidence.
“The Sandvik breakers are extremely well built, easy to maintain and are inexpensive to run. But best of all, they come with the expertise and knowledge of the Sandvik breaker support team, and that is invaluable on a project like this,” Mark Kime concludes. “In fact, we’ve been so impressed by the support we have received, we've just ordered two new Sandvik screens.”