Circular Service Reservoir Refurbishment

Stonbury were to complete refurbishment works to a service reservoir dating back over a century to give it an additional 30-year lease of life at a fraction of the cost of building a new one.

This 20.5ML balancing reservoir was built in 1913 and was originally built as an open tank for clean water storage, after regulations changed, the circular tank was enclosed with a steel-clad roof. Recent investigations discovered water ingress to the tank and the existing brickwork walls were found to be in a poor state. Stonbury were commissioned to undertake a comprehensive internal refurbishment together with some external repairs.

The project came with a number of challenges – not least carrying out work on the roof internal, where roof vents were allowing in rainwater. This required erecting scaffolding and an extensive area of safety netting. External access to the roof also posed safety risks as the roof had a low load bearing capacity. In addition, the contract came with a tight deadline of just 12 weeks because of the need to get the reservoir back into use to meet the higher customer demand of water in late spring.

The client specified a very high quality surface internal finish, ensuring that the reservoir will enjoy the maximum service length after completion. Stonbury assigned a team of 15 full time personnel to the project, including specialist contractors for the steel fabrication and construction of new stainless steel stairs within the reservoir. The project commenced with overbanding to the floor joints, applying the longer lengths first while keeping the joints clean ready for the welding. Ultimately, some 3804 metres of overbanding were required to cover the 3849m2 of flooring creating a spider web effect in the circular-shaped reservoir. Priority was given to completing the joints near the flume first, so it could be fixed back into position.

At the same time, another team commenced grit blasting the walls to prepare them for resurfacing, as well as cleaning the other surfaces; including the steelwork within the reservoir. Work started first on the walls at the lower section, allowing regular checks on the profile to ascertain if the amount being removed was adequate and even.

A detailed survey of the roof vents (which had been allowing in rain water) and the grating to the floor channel to determine the scope of work required. By week 6 of the project, the overbanding to the floor of the reservoir had been successfully completed, and the internal surface of the reservoir walls, comprising Staffordshire blue engineering bricks, had been sufficiently prepared for mesh to be fixed to the walls across 24 bays and a total area of 1200m2. Fixing the mesh, which ultimately took a total of 15 days, created a suitable surface for the concrete spray to be applied. In total, 55,000 litres of concrete spray were applied to the perimeter walls. Timber screed rails were then fixed into place and spraying of the reservoir walls began in week 5, once the mesh had been applied in the first few bays.

A separate team erected scaffolding and fixed safety netting to the internal roof, providing safe internal access to the vents. Steel fabrication contractors also came on site to install a series of channel covers inside the reservoir. Because the metal roof would not safely withstand the weight of people working on it, scaffolding was erected in several places over the top, together with a series of safety lines to provide safe external access to the vents. With the roof vents fixed in place, a Davit Arm and an SS ladder were introduced; and these, together with the scaffolding, provided safe access for the internal steel surfaces in the roof to be coated.

With the concrete spraying nearing completion, work then commenced on the perimeter walls overbanding, applying some 120m of overbanding to seal the joints between the 24 bays. In the final week, final tests conducted to ensure the water tightness of the overbanding and the site cleared and cleaned ready for inspection. A new handrail was installed on the top landing area and bracing applied to the newly installed access ladder. The final inspection was conducted by the client and the project was deemed completed and handed over.

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