A bespoke design feature and horrendous ground conditions have put Willmott Dixon to the test in Hampshire.
Project: Hart Leisure Centre
Client: Hart District Council
Contract value: £23m
Main contractor: Willmott Dixon
Steel frame subcontractor: Conder Allslade
M&E subcontractor: CMB
Roofing subcontractor: SIR
Cladding subcontractor: SIR
Start date: September 2015
Completion date: February 2017
“I’ve never had scuba divers at work before, and I’m not sure I ever will again,” Richard Weaving concedes.
Unusual additions to the site team are far from the only aspects of Hart’s new leisure centre that make it stand out, according to Willmott Dixon’s senior site manager. A high water table, frustrating groundworks and complex structural issues have been among the challenges the contractor has had to surmount so far.
And as Willmott enters the final months of the programme, its site team is gearing up for what may prove to be the most challenging aspect of all: installing a swimming pool with a moveable floor.
Swampy and the countless trousers
Long before the prospect of scuba divers on site loomed into view, the contractor first had to deal with extremely difficult conditions when it started on site back in September 2015.
The £23m development in north-east Hampshire is focused on a main centre comprising a sports hall, three swimming pools, a gym, spa facilities and a climbing wall. The 3 ha site will also feature five 3G synthetic grass sports pitches, two large multi-use areas, a full-size grass pitch and a 300-bay car park.
“It was just a field when we got here,” Mr Weaving says. “We knew the water table was very high – even just walking across it, you could quite easily sink up to your knees.”
Willmott Dixon Hart Leisure Centre 19
The team identified rapid roll-out of temporary roads as crucial to work proceeding. “In the end we didn’t use as much of the temporary works package because we got the roads in early,” he says. “Driving mostly on tarmac rather than the actual mud has saved us so much time in terms of disruption, sinking dumpers and so on.”
While the roads have helped protect equipment, the site workers have not always been able to escape the mud. “We were spending so much time pumping water out the ground,” Mr Weaving explains.
“You’d go in the pools on a Friday and they’d be empty; you come back Monday and there’d be 2 ft of water in there”
Richard Weaving, Willmott Dixon
“Around Christmas it was very bad weather, so when digging foundations you had to be ready for the rebar crews to be in there that afternoon – if you left it any longer, the sides would just slip away and the hole would fill up with water. We had as many as 10 submersible pumps pumping away all the time.”
There site required around 100 mass concrete foundations 2-3 m deep, with the pool structures themselves more than 2 m deep.
Unsurprisingly, the pools’ excavation proved particularly tricky: “You’d go in the pools on a Friday and they’d be empty; you go away for the weekend, come back Monday and there’d be 2 ft of water in there, just groundwater pouring in, and sometimes the rain over the weekend.”
Removing water from the site required a herculean effort from the team. A ditch runs along the back of the site, which was dredged and cleaned. When the team pumped out a foundation, the water was directed straight to one of several Siltbusters positioned around the site before entering the ditch.
Willmott Dixon Hart Leisure Centre 14
“The amount of water was extremely challenging,” Mr Weaving says. “We were just covered, every day, all of us were – we were going through trousers like they were going out of fashion.”
The conditions claimed one particularly famous victim. An apprentice acquired the nickname ‘Swampy’ after returning to the site office in his socks having lost his boots to the unforgiving mud. “That’s a bit of a running joke,” Mr Weaving explains. “That’s gone around the company now – everyone knows him by ‘Swampy’.”
Lessons help prep for scubas
It’s not just tales of unfortunate trainees that travel around Willmott Dixon. As a contractor with a sizeable portfolio of leisure centre jobs, Willmott’s internal comms provided the Hart team with guidance and drove earlier engagement.
“If the ropes were let go, the floor would just float up and be level with the top. You hit a button to adjust the pulley and it pulls the floor down”
Richard Weaving, Willmott Dixon
“When we got here we pulled off a lessons learned folder from the Willmott Dixon intranet,” Mr Weaving explains. “We’ve done lots of leisure centres across the country and we sent this folder out to our consultants, asking them whether we faced these issues and to tell us what they’re doing to resolve them. So when we finally got going, we’d already ironed out a lot of issues already.”
Even when not caught beforehand, the team’s rapid approach to solving problems has been crucial, as illustrated by a major issue affecting the leisure centre’s roof. “When we started to clad the roof, we found that some of the steels were higher than the others to the left and the right.
Willmott Dixon Hart Leisure Centre 20
“You couldn’t find that out until you started laying the sheet. One steel was 38 mm higher than the rest. The steel frame was within BS standard tolerance but the steel sheets could only take a tolerance of 12 mm differences.
“We stopped and went back to engineers; a week later we’d got the design resolved, adjusted the steelwork, everybody signed off and we started progressing slowly. It took around three weeks in the end but it’s all done now. That was another lesson learned and uploaded to the intranet.”
‘I thought it’d be hydraulics’
Willmott Dixon’s resources are proving especially handy as the team prepares to deliver what is perhaps the centre’s most eye-catching feature: a swimming pool with an adjustable floor to cater for different swimming abilities and activities.
Mr Weaving admits it’s a first for him and his team, but fortunately help is at hand. Another Willmott project in St Albans also features an adjustable-floor pool, and Mr Weaving will soon be paying a visit to Hertfordshire to prepare for the installation.
“I’ve never used BIM as much as I have on this project. We walked through all the clashes, and it’s saved us so much time”
Richard Weaving, Willmott Dixon
In the meantime, several stages must come together ahead of the pool floor being put in. “Once the pools are filled up towards the end of October, the pipework will start to be turned on, which will start heating up the water a little bit for the scuba divers,” Mr Weaving says.
“The steelwork will have been dropped in first. All the other bits [of the installation] are done by the scuba divers.”
The adjustable floor is made up of small trolley jacks and operated by a pulley system. “I thought it’d be hydraulics, but it’s not,” Mr Weaving says. “If the ropes were let go, the floor would just float up and be level with the top. So when you want it down to a certain height, you hit a button to adjust the pulley and it pulls the floor down to where you want it.”
Tangible BIM benefits
Such bespoke elements have required huge amounts of forward planning – something that has been boosted across the project by extensive use of building information modelling.
“Everyone’s on the Revit model,” Mr Weaving points out. “I’ve never used BIM as much as I have on this project. We walked through every room, through all the clashes, and it’s saved us so much time.
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“We don’t have the usual problems with a bit of a steel poking out or a plug that can’t go where it needs to; it’s just so easy now, I love it. If someone asks me a question, it’s all in the model – it’s one of the first things I look at every morning. The next step for me is to have a Revit model on a tablet out on site – that would be cool.”
The next steps for the contractor include completing the pools, making the building watertight and polishing off final landscaping, as the team moves towards its February 2017 completion date.
And the Willmott team is confident that the lost boots, roof hold-ups and scuba diving will all be worth it when the firm hands over what promises to be a worthy addition to its leisure centre portfolio.
Missile-style system causes concrete headache
Willmott Dixon hails the relationship it has had with the client, Hart District Council, and particularly its leisure manager Carl Wesby.
At preconstruction stage, Mr Wesby had wanted to use an innovation called Poseidon – a camera system that monitors swimmers from the pool hall ceiling. “The easiest way to describe it is that it’s like missile detection technology: it tracks people’s bodies in the pool, and if they don’t move for a certain amount of time it triggers the alarm and shines a light on where they are in the pool for the lifeguard,” Mr Weaving explains.
However, the company behind Poseidon came back to Willmott with a figure nearly double what Mr Wesby had been told, so he turned to another camera system called Pool View, which needed to go into the structure of the pool wall.
“At that point, we were pouring the walls,” Mr Weaving recalls. “So we stopped pouring, met with Pool View and found that they didn’t do their own containment as part of the installation. We went to our mechanical contractor and did a sample run with flexible conduits, which leaked like a sieve when we did a pressure test on them.
“I did some research and found that the product we were trying to employ was being used on another Willmott project in High Wycombe.”
That project had faced similar issues, allowing the team to once again learn lessons and find a solution for the client. “We ended up using polypipe with connectors on it to solve the issue. That affected [the programme] by three weeks; the client has given us an extension of time, but we feel we can still hit our original completion date.”