Water and Effluent Treatment Magazine
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12 WET NEWS JULY 2014 The innovative girder trusses to help reinforce the steel "Ultimately, health and safety is what drives our decisions, our designs, all our processes. A zero tolerance approach in construction. That's been a real cultural shift for Thames and GBM over the last AMP." Neil Franks, Thames Water ONSITE Service Reservoir at but there were con- cerns over it being a bur- ied structure. Metal reser- voirs are perfectly fine, says King, but its more the long-term maintenance and structural integrity meant the whole life cost numbers did not add up. King says: "With a 100-year design life on the reservoir con- crete always wins over steel because you can guarantee that." Even when it was decided that build would be done in- situ even that changed at the start of this year. The project has an in-situ base and walls; pre-cast columns; a composite element of pre-cast and screed on the top; waterproofing on the roof; topsoil; and grass. The process has quickened the programme to a point, but now "we're running out of space". King explains: "Space on this site is so tight. The embankments we cut to get down to the base are as steep as we could physically build them. "We cut them between August and November last year, so they stayed up through the winter but they wouldn't last another winter. "We always knew that. We just had to push on with the build and know that within five weeks we can start backfilling in." Design-wise, the process has been the most efficient way of doing it in the centre of Lon- don, says King. About 4,500m 3 of concrete has been poured so far and "we still can't guarantee the time it will take to pour the concrete because we can't predict what the traffic will be like in the road". All concrete pours are down to 30-40m 3 . The pours could have been bigger but there was no guarantee the concrete would get poured in a day. "We're getting slots in and planning, and that changes every week. It's purely where we are. The concrete is batched three miles away." Health and safety also has to be taken into consideration. Franks says: "Ultimately, health and safety is what drives our decisions, our designs, all our processes. A zero tolerance approach in construction. That's been a real cultural shi• for Thames and GBM over the last AMP." The reservoir walls are 6.5m high, and you cannot go much further than that without hav- ing a joint in the wall. A key and innovative way to reinforce the wall has been the use of girder trusses in the steel in the walls. The trusses are welded into the starter bars, and so all the walls will be steel-fixed with not a single prop used. King believes the girder truss system "has got the potential to be an industry standard. It's helped us get ahead and know exactly where we're going to be pouring. King says there has always been systems for holding steel up but it "generally involves a lot of money and a lot of steel". Instead, the girder truss zig- zags in the steel. O•en it's the simple things that are most effective, and that's [the truss] is innovation. "In essence, we're building a concrete box and burying it! It's a nice civil engineering job but when you get something like the truss system that's proven itself that's the best thing I've learnt from here." Apart from not being big enough, other challenges included not being able to store backfill onsite. About 22,000m 3 of soil dug up had to be taken offsite, and 10,000m 3 will be brought back. A standard filter drainage will be implemented at the reser- voir, and GMB will have to ensure there is no run-off going into the park. Sustainable urban drainage will also be used. "We need to know exactly what's happening every single day, but it's changing constantly." Weather With the site running out of space as the project finishes, everything has got to be planned out. "About 99% is planned to the nth detail but it still needs chopping and changing." Loads are now being taken on site on short vehicles because there is less space and some are having to be moved with a crane. The recent hot weather has presented its problems as meas- ures had to be taken to prevent the concrete from drying out too quickly. But the winter "was kind to us". Franks says: "In January, February we didn't get the ground frost or the snow but we got the two feet of water that we knew we would get." King says: "We shut down. We knew that was going to hap- pen because we were lower than any of the drainage, which was not connected, and it's London clay. It holds water like a reservoir! "Although the autumn was horrendous, we were doing the muck shi• then, rather than pour concrete. If it had been the year before, we could have been pouring concrete all winter whereas it's worked better as we started in February and all the concrete's going to be in over the next four weeks. "It's all going the right way at the moment." GMB's Allan King (left) with Neil Franks, of Thames Water The submarine doors will make inspections easier GMB starts filling one cell to ensure there are no problems. Filling the tank was expected to take a week SHARE YOUR OPINION... yoursaywn@fav-house.com