WET News

10 WET NEWS MAY 2016 I n 2012, MVB – a joint venture between Morgan- Sindall, Vinci Construction Grands Projets and Bachy- Soletanche – called in Asset International and Uponor Project Services to examine a complex design proposal to help resolve London's age-old sewage problems. MVB had been appointed to construct Thames Water's four- mile Lee Tunnel, to prevent 16 million tonnes of sewage from homes and businesses in the capital entering the River Lee – a tributary of the Thames – each year during heavy rainfall. This longstanding headache for London's planners had resulted from an outdated Victorian sewerage network being unable to cope with the increasing demands of a highly-populated twenty-first century city. The £635M Lee Tunnel is one of three multibillion-pound engineering schemes designed to prevent sewer overflows and improve water quality in the Thames. The largest of these is the £4.2bn Tideway Tunnel 'super sewer.' The 7m diameter Lee Tunnel captures discharges, following heavy rains, from the Abbey Mills Pumping Station in Stratford. The tunnel then transfers these flows to Beckton sewage treatment works, which has been vastly expanded in order to deal with the increased volumes. Asset International was also heavily involved in the £190M Beckton upgrade project back in 2013, and its Weholite high density polyethylene (HDPE) resin pipes of multiple Taming the Thames • The UK's first ever sub-sea installation of a sectional installed, multi-directional, sewage pipeline will help tackle London's outdated sewerage network. Asset International's Dr Vasilios Samaras reveals all. ONSITE PIPeS dimensions were used to help expand the facility's capacity by 60%. Tidal protection Asset and Uponor PS were asked to develop designs for the outfall element of the Lee Tun- nel pipeline, which would carry raw sewage up-river to the Beckton works. As well as ser- vicing the Lee Tunnel outfall, the Weholite solution will also provide the final discharge point for the Tideway Tunnel. The Lee project was divided into two specific elements – land and marine. The land element required 105m of Weholite twin culvert pipes laid at depths of 10m. This operation had the added complication of needing to break through the tidal protection wall that stops the Thames flooding the Beckton works. However, our team resolved the problem by using a giant 7m x 11m x 5m Weholite Modular box to house two 3,000mm spool sections to complete the installation without compromising the tidal wall. While the land element of the project was far from straightforward, the marine element presented even bigger challenges. One of the contractor's original options for achieving the project goals included building a concrete box culvert in a dry trench on-site by holding back the tidal waters of the Thames; a river which experiences a tidal rise and fall of 7m each day. However, these plans were dismissed early on by the projEcT SpEcS • Install a multi-directional, sewage pipeline • Develop designs for the outfall element of the Lee Tunnel pipeline • Install 335m of twin culvert pipeline contractors themselves, who then turned to the Asset and Uponor PS partnership to re-engineer the project and come up with a new solution. This partnership ultimately created a landmark design – the UK's first ever sub-sea installation of a sectional installed multi-directional sewage pipeline. It also became the biggest plastic outfall ever installed in the UK, comprising a total of 880m of 3,000mm diameter Weholite HDPE pipes and 12 large-scale Weholite Modular HDPE boxes. Moreover, it was one of the biggest in terms of diameter worldwide. The operation to install 335m of Weholite twin culvert pipeline into the dark tidal waters of the Thames was carried out by specialist contractor Commercial Marine & Piling (CMP) working alongside the Asset / Uponor PS partnership. Timings This already ambitious marine project was further complicated by the fact that the pipes needed to be submerged under an exist- ing jetty structure, and sections of the project were o¦en iso- lated by the tide, with no access from land. This meant that tim- ings needed to be meticulously planned to synchronise with the ebb and flow of the tide by CMP. All the Weholite pipes and modular boxes were manufactured and prefabricated at Asset's Newport, South Wales factory. The pipes were then delivered to London Docks, in 18m lengths, before being welded into 'strings' of up to 90m. The 50-tonne strings were then li¦ed onto the water using three mobile cranes, working in tandem, before being prepared for towing by tugboat to the submersion site by CMP, around 3km up-river. One of the key elements involved in using Weholite products to deliver this project was the utilisation of Uponor's patented grouting process. Probably the most relevant feature of Weholite is the ability to mortar-fill the pipes' hollow profile wall. For this purpose, different density materials can be used to counterweigh the pipe, reaching up to 20% in weight against the upli¦ing force. This is a patented method based on injecting a mixture into the pipe's profile with several additives that keep the injected material so¦ and supple. Every day more than 60m of the Weholite pipes' hollow profiles were filled, an incredibly fast and efficient process, conducted using a vacuum pump connected to a grout lorry. There are several main advantages in using this method for marine conditions: • Different materials can be chosen depending on the extra weight required – eg cement, mortar or limestone • It offers up to 20% of counterweight • The filling material is much cheaper than concrete and the pumping is fast • The pipe maintains its flexi- bility, even with its hollow pro- file filled A direct consequence of the profile filling, and the one Three mobile cranes were used to lift the pipe strings on to the water

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