Water & Wastewater Treatment

18 | APRIL 2016 | WWT | www.wwtonline.co.uk Project focus: sewer networks The proposal to overcome this enormous challenge included 880 metres of 3000mm diameter Weholite pipes laid as a twin culvert along with twelve large-scale Weholite Modular HDPE boxes, and the provision of installation, supervision, site services and health and safety management. As well as servicing the Lee Outfall Tunnel, the Weholite culvert will also be the final discharge point for the prestigious £4.2BN Thames Tideway tunnel. Construction of this 'super sewer' started this year and is scheduled to complete in 2020. The project was divided into a land section comprising of 105m of twin culvert laid at 10m depths. This section had the added complication of needing to break through the tidal protection wall that stops the Thames flooding Europe's largest treatment works at Beckton. This issue was overcome by utilising a giant 7m x 11m x 5m Weholite Modular box to house a 3000mm spool section to complete the installation. The operation to install the remaining 335 metres of twin culvert section into the black waters of the Thames was carried out by marine contractor Commercial Marine & Piling Limited (CMP) alongside the Asset and Uponor PS partnership. However, this ambitious marine project was complicated still further by the fact the pipes needed to be submerged under an existing jetty structure and sections of the project were o˜en isolated by the tide, with no access from land. All the Weholite pipes and modular boxes were manufactured and prefabricated at Asset's south Wales factory. The pipes were delivered to the historic London Docks site, in 18 metre lengths, and were • Perspectives Thames Water chief executive Martin Baggs: "While the Victorian system still works very well, it needs additional capacity to cope with 21st century London. The Lee Tunnel and, when completed and connected, Thames Tideway Tunnel, will together capture the tens of millions of tonnes of sewage that currently overflow untreated into the tidal Thames every year. This will protect the future of the iconic river and capital for future generations." Emmanuel Costes, construction manager at MVB: "We were very happy with the Weholite technology employed in the implementation of the Lee Tunnel Outfall pipeline. The specifications of the project were very particular, however the solutions provided by the Asset International/Uponor collaboration were impressive, ticking all of the boxes that this complex, and in many cases unique, project demanded." Christian Vestman, Uponor Project Services: "The Uponor Asset Partnership demonstrated the full depth of knowledge and versatility available within our organisation. This unique project really allowed us to showcase the impressive capabilities of Weholite and the results speak for themselves." The land section of the HDPE outfall welded into strings of up to 90 metres. The 50 tonne strings were then li˜ed onto the water using three mobile cranes in tandem and prepared for towing to the submersion site, around 3km up river. Part of this preparation involved utilising Uponor's patented grouting process. This innovative methodology eliminates the need for heavy concrete collars to ballast the strings. This traditional way of installing marine pipelines can o˜en be extremely risky during submersion. Filling the hollow Weholite profile with an inexpensive and pumpable grout is much safer and affords for a much quicker preparation time. With no concrete collars a smaller trench is needed, the dredging operation is minimised and the volume of excavation is therefore drastically reduced. Since submarine excavations are much more expensive than on dry land the advantages of Weholite are transparent. By using the grouting system, Weholite submersion is much easier to control and ultimately safer. Once the pipe strings were ready, they were towed individually up river by tugboat and then submerged. Specialist divers were used to bolt up the innovatively designed quick connect flanges that joined each pipe string. The project also included installation of over 11,000 m 2 of steel sheet piling to allow the dredging of the river bed so the pipes could be laid free from obstruction. Over 28,000 m 3 of riverbed materials were dredged and much of the dredged materials were reused to backfill the pipes once installed. This provided an environmental advantage by vastly reducing the amount of materials to be taken off site, thereby saving on the carbon footprint. The London Tideway improvements are but a few of the most impressive and ambitious engineering projects to be undertaken in the UK in a generation, perhaps since the Victorians themselves built the very sewers that Thames Water are currently upgrading. It is a fantastic example of world leading British engineering at its best, and a project that Asset International is extremely proud to be a part of. The scale and scope of the installation means that not only has it become the UK's largest plastic outfall pipeline, but it also represented the UKs first ever sub-sea installation of a sectional installed multi-directional sewage pipeline.

• Cover