Water & Wastewater Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/670690
16 | MAY 2016 | WWT | www.wwtonline.co.uk Project focus: Pumps and pumping systems for the required pump station storage, while two new 7.5kW submersible pump units would deliver the necessary flows downstream. In addition, the refurbishment of the existing emergency overflow chamber included a new static bar screen that would also serve to provide additional resilience against potential future pollution events. In order to achieve the build within a restricted compound, and also taking into account the adjacent site of ecological importance, the team decided that the only way to • Innovations ● Prefabricated units constructed off-site, overcoming restricted space on-site. ● Project completed two to three weeks quicker than traditional construction methods. ● Site waste reduced by three quarters. The li chamber at the new pumping station at Heage the design meant that on-site construction took just 11 days to be completed. The general timetable was excavation on days one to four, with the valve chamber installed first, followed by the Weholite chamber on day five. The tank was then filled with water a-er installation to prevent upli- and to aid structural stability during concreting. Days six to 10 saw five concrete pours (one on each day) to produce a 1m surround that was allowed to cure over the weekend. The final activity, on day 11, was to set the pre-cast cover slabs in place and to install guide rails and pumps, and to finish off the duct work. In total, we estimate that, by taking this approach, we saved two to three weeks in comparison to other potential, traditional construction routes. Factory thinking approaches led to a safer assembly, which helped reduce the overall health and safety and environmental risk from on-site construction, and the quality controlled prefabricated environment also helped guarantee consistent products. Being able to cut the construction period to just 11 days on site also saw reductions in stakeholder and customer disruption, as well as ensuring a reduction in accompanying costs. Alongside the operational benefits associated with the new pumping station, the decision to construct using prefabricated section also helped with the project's environmental benefits. Site waste was reduced by almost three-quarters when compared with similar sized schemes, with 100% of the waste recycled off site. There was also a significantly reduced carbon footprint in comparison to a more traditional concrete pumping station solution thanks to the reduction in length of the overall construction programme and the use of recycled materials in the manufacture of the Weholite wet well. The 120-year design life of the wet well should also ensure that all future site work is limited to simple maintenance and minor modifications. While the decision to use an off-site prefabricated design was necessitated by the nature of the site at Heage, it was clear by the end of the project that, in terms of quality control, reduction in construction timescales and improvement in environmental impact, there are potentially huge benefits in using this method for similar sized projects that are less constrained. The precast concrete cover slab arrived with pump access covers achieve all of that was to go with off-site prefabrication, with only final assembly and connections taking place on site. That meant the concrete valve chamber and the Weholite wet well were both constructed entirely off site and then shipped to the compound to be 'slotted' into place. In fact, the Weholite wet well chamber came complete with fittings, the precast concrete cover slab arrived complete with pump access covers, and the precast valve chamber was fully fitted with valves, pipework, flowmeters, access ladder and open mesh flooring. The designers also had ease of long-term maintenance at the forefront of their minds, with the inclusion of new covers providing the safest possible access arrangement, and a new li-ing davit system. A new upstream inlet manhole to isolate and divert flows was also included. Severn Trent then also modified the existing control panels to include level instrumentation and flowmeter telemetry to provide us with real- time operational information which is used to monitor and review the station's performance. The innovative nature of