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Case Study – Rapid Gravity Filter (RGF) Replacement, Derbyshire

Case Study – Rapid Gravity Filter (RGF) Replacement, Derbyshire

New RGF Installation Saves £500,000

Main Contractor: Severn Trent Water

Long-standing clients Severn Trent Water were tasked with the refurbishment of six Rapid Gravity Filters (RGF) in Bamford, Derbyshire, as part of a £5 million design and build contract.

Contractors Stantec Treatment (formerly MWH Treatment Ltd) put forward a case to build two brand new RGF’s rather than refurbish the six filter systems currently in service. Stantec demonstrated it’d be considerably cheaper and would provide an improved service.

The solution required a 11.85m x 33.8m x 4.56m deep cofferdam following a local 2m ground reduction. Land boundaries, hard ground/rock level, weight restrictions and the disruption of other underground services were all stand out elements to consider in the design. Extra care was taken during the planning of the excavation to avoid the disturbance of a water main running just 2 meters away from the edge of the site.

RGF shoringSite excavation showing diggers, MGF sheets, braces and Edgesafe equipment









The boreholes provided in the location of the works highlighted hard ground around the final toe-in depth of the shallower sections of the cofferdam. At the request of the Engineer, MGF sent test piles to confirm driveability and to check that the required toe-in could be achieved. A second frame was installed in the deeper section of the excavation as a propped cantilever solution was not feasible.

MGF’s Engineers are committed to finding a solution that provides the client with the most cost-effective and practical design to meet their temporary works requirements. A significant saving on cost and time was highlighted at the initial site meeting by designing as a split-level excavation.

Chris Trotter, MGF’s Technical Sales Representative, explained the key benefits to the contractor:

“Once the lower structural base slab was cast, the lower frame was removed and off hired leaving only the top frame (propped cantilever at the 2nd stage). Once the upper structural base was cast the top frame was removed leaving the piles in cantilever at the 3rd stage.

The contractor was able to carry out formwork without any shoring frames in the way. This solution saved the client unnecessary hire costs and allowed a better workspace.”

Replacing the RGF’s with two brand new systems was successful and is estimated to save £500,000 on the planned project cost, thanks to the proposal by Stantec Treatment.

Overview of large excavation with MGF hydraulic braces, sheets and Edgesafe products installed

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