Building five pools and a football pitch in south London


With movable swimming-pool floors, a football pitch perched on top, and 105 metres of waterslide, Morgan Sindall is having a lot of fun building the Woolwich Leisure Centre

Contract: NEC 4 Option A
Project value: £80m
Main contractor: Morgan Sindall
Client: Royal Borough of Greenwich
Framework: Southern Construction Framework
Engineer: Buro Happold
Architect: FaulknerBrowns Architects
Demolition: Redhammer
Groundwork and reinforced concrete: Mitchellson Formwork and Civil Engineering
Steelwork: Elland Steel
Curtain walling: Drayton Windows
Swimming pool: FT Leisure
M&E: Halsion
Construction start: April 2021
Construction handover: October 2025

Woolwich’s history has long been bound up with water. It is home to one of the capital’s oldest river crossings –  the first records of the Woolwich Ferry date back to the 1300s – and was chosen by King Henry VIII to moor his navy’s flagship.

The Royal Borough of Greenwich is continuing the aquatic theme as it takes the district into its next life stage. The heart of the council’s regeneration strategy is an £80m leisure centre, with the focal point a state-of-the-art swimming complex.

When it opens in 2025, Woolwich Leisure Centre will host five swimming pools, a spa, a six-court sports hall, a five-a-side football pitch, a two-level gymnasium, dance and spinning studios, two squash courts, a cafe, a soft play, party rooms, studio spaces and a district energy centre – all on a 12,000 square metre plot of land.

Having successfully delivered multimillion-pound leisure centres in Slough, Worthing and east London, Morgan Sindall turned its attention to southeast London. It hasn’t all been plain sailing. Not only is the site compact, but it also has some pesky neighbours: a busy bus station, a listed theatre and a 500-home project being constucted by housebuilder Hill Group.

Foundations

Cleaning and heating the million litres of water needed for the pools takes a lot of plant. Housing that plant under the floor required a mammoth excavation. The 1,800 square metre basement will hold a 190 square metre UK Power Networks substation and low-voltage plant room, 1,360 square metres of plant for the pools, including filtration and balance tanks, and a 250 square metre energy centre to heat the leisure centre, the Tramshed theatre (a 100-year-old Grade II-listed former electricity substation) and the residential development.

The new leisure centre is being built on the site of Viscount House, latterly a Wilko store, on General Gordan Square. As soon as the team started enabling works in April 2021, they ran into a problem – there were no records of how the previous structure was made.

Engineering firm Buro Happold carried out trial excavations, discovering that the previous building’s foundations were mostly mass-filled concrete, bedded on Thanet Sands. But there was a catch: the foundations completely surrounded the foundations of the neighbouring Tramshed theatre. This meant that removing the mass fill for piling was not feasible. Instead, Buro Happold designed new 4-metre-deep foundations that incorporated the existing foundations.

Piling subcontractor Foundation Piling removed one side of the blockage by coring a secant-pile formation 4 metres through the mass-fill concrete. The team then backfilled the area and drilled continuous flight-auger piles 6 metres deep. The piles were cantilevered to avoid deflection without needing props.

The complicated foundations weren’t the only subterranean surprise – the team also spent £1m diverting underground services. “Every time you do a project in London, you don’t know where the services are,” says Morgan Sindall senior project manager Mike Perera. “Even service providers don’t know where the services are.”

Despite all the obstructions, the team dug out 11,250 cubic metres of material in six weeks. Construction-waste specialist GRS took around 50,000 tonnes of soil and stones – more than 95 per cent of the excavated material – to its aggregates processing plant in Tilbury, Essex. There it washed and segregated the materials before recycling them into shingle aggregate and sharp sand to use on other local construction projects.

Building five swimming pools to last 40 years is a big ask. Each pool comes with precise requirements and specific engineering challenges. The competition pool, for example, is designed to Sports England standards, requiring it to be exactly 25 metres long. If the measurements were one millimetre off, the team would have to demolish their work and start again.

Mike King, construction director at concrete subcontractor Mitchellson, says that the firm took a “belt-and-braces” approach to designing and building the concrete shells of the swimming  pools in order to meet the high standards set out before them.

“It was a lot of work coordinating between ourselves, Morgan Sindall and [swimming pool subcontractor] FT Leisure to incorporate the M&E [mechanical & electrical] elements into the reinforced concrete – way above what we normally do,” says King. “Everything is checked before and after every concrete pour – once you’ve done it there’s no going back.”

A total of 49 pours for the basement foundations, basement slabs, liner wall, main swimming-pool slabs and training-pool walls were completed between October last year and this January, involving 3,600 cubic metres of waterproof and standard concrete.

Waterproof concrete pouring continues for the transfer channels in the main pool and training pools, main-pool walls, and the leisure and toddler pools. These require more than 40 pours and a total of 665 cubic metres of concrete, Construction News understands.

Mitchellson used a waterproof additive in the concrete and installed waterbar on all the construction joints. To ensure the structures were sealed from the point of construction they choose traditional waterbar over hydrophilic strips, which become watertight over time by swelling in contact with water.

Wet and dry separation

Key to avoiding leaks and spills is maintaining a strict separation between wet and dry areas. The five pools, spa facilities and wet changing areas will occupy the first floor of the leisure centre, with the sports halls and exercise studios sitting above.

Putting the two so close together is still a risk. “The chlorine-rich atmosphere [of the swimming pool] is really corrosive,” says Morgan Sindall area director Richard Dobson. “Any metal that is not the right grade will just corrode.”

Materials were carefully selected to provide a strong barrier between different areas. Glass-reinforced plastic doorsets are a waterproof and corrosion-resistant alternative to wood or metal, and cellular glass board insulation provides a fully sealed vapour barrier.

Curtain walling used internally forms another vapour barrier. The joints will be sealed with EPDM (ethylene propylene diene monomer), a waterproof and durable synthetic rubber.

Architect FaulknerBrowns originally designed a roof with 80 penetrations. Morgan Sindall worked with Buro Happold to redesign the roof steelwork, whittling that number down to four. “Eighty penetrations means 80 places leaks can happen,” says Dobson.

Steelwork to hold a football pitch

Putting a football pitch on the third storey of a building is not an obvious move. The building’s frame must be particularly sturdy to withstand all the vibration from an energetic game, but engineers can’t just place more columns in the middle of the pitch without getting in the way of the action.

Buro Happold, which engineered the 1,200-tonne steel frame, used purpose-built software to model the dynamic response. Steel beams are optimally sized to provide stability over long spans.

A 40-tonne truss over the sports hall will help stabilise the structure while still allowing for a large free floorspace. A 36-tonne truss will support the roof over the leisure waters, while 25-metre-long plate girders measuring 1,800 by 650 millimetres will bolster the roof over the competition swimming pool.

Going swimmingly

When the high-level areas (ceilings, walls, M&E and decoration) are completed in early 2025, it will then be time to install the leisure centre’s pièce de résistance – 105 metres of waterslide. The two flumes will be lifted in section by section with spider cranes and put together by workers in cherry pickers. Tiling will then be completed to the areas that were not finished due to spider crane positions.

High-end finishes to the pool areas are integral to the design. High-quality tiling is much easier to clean and maintain – once the leisure centre opens in December 2025, with extended hours there won’t be much time for touch-ups and maintenance.

This entails a boatload of tiles – 10,800 square metres, to be exact. Each tile, of which the largest is 1,200 millimetres by 600 millimetres, has to be installed to a high level of tolerance to meet exacting hygiene standards.

Morgan Sindall has yet to appoint a tile installation subcontractor, but it will have to be comfortable with a range of tiles. Glazed ceramic tiles will be used within the pools for a smooth finish, while the poolside-area finishes require slip resistance. The contractor expects to employ around 30 tilers to complete the job. “Managing [so many] tilers is a project in itself,” says Dobson.

Once the pools are built, they will be tested for watertightness one at a time, reusing the same water to avoid waste. Two shallow watertight evaporation trays will float in each body of water, filled with 75 millimetres of water. The water level in the pools and trays will be recorded every 24 hours over a seven-day period. Any leakage will then be calculated by comparing the water loss from the pool basins with the water loss within the evaporation trays.

Despite all the intricate engineering required, the team has really dived into the challenge.

“Leisure centres are so many mini-projects within a bigger project,” says Perera. “I can’t see myself wanting to go back and do office jobs and laboratories.”

Variable depths

Two of the pools will feature floors that can be raised and lowered, allowing different water depths for different activities. For example, there will be waist-heigh water levels for aquaerobics and toddler-friendly depths for swimming lessons.

Once all the piles have been installed, Dutch moveable-floor specialist Variopool will bore holes into the basement and set up hydraulic rams and hydropowered water pumps, which will lift the floor up and down. It will then install temporary props and fit the platform on top.

Mechanical and electrical subcontractor Halsion will coordinate with Mitchellson to fit the ventilation systems, making it possible to heat and clean the water without producing condensation.

When the water temperature and cleanliness are signed off, divers in full scuba gear will climb under the platform through a hatch and take out the props, allowing the platform to move up and down.

“If our walls are crooked it won’t work,” says Perera. “Think of putting your hand through water – how much force you need. Imagine that with a platform.”



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