Water & Wastewater Treatment

PIPES AND NETWORKS 31 February 2014 Water & Wastewater Treatment wwtonline.co.uk 315mm SDR 17 to adjust the materials used to the pressure rating required. Thatcher continues, "One of the major advantages of using PE pipe is that the diameter and wall-thickness of the pipe can be tailored to meet the ground conditions and water pressure at different points along the pipeline. In this case, there was a 50/50 split between the two pipe sizes so the complexity of the project lay not in multiple pipe sizes, but in the no-dig installation requirements along 30% of the route." Installation challenges Optimise completed the open-cut installation work first, butt-fusing lengths of pipe together and laying the strings into each section of trench. They used 10mm of recycled pea shingle for the pipe bed and surround before back-filling with the excavated material. The ground in the area is a mix of chalky soil, gravel, flint and sand, which was easy to excavate for the open-cut areas of the installation, but created challenges for the directional drilling (DD) element of the project. Thatcher explains, "In some areas we had to drill as deep as 3.5m to avoid any disruption to obstacles along the route and the sandy, chalky ground combined with the sharp-edged flint and gravel meant that we had to take our time to avoid any unnecessary abrasion to the pipe." Amongst the areas where Optimise had to drill to 3.5m were the stretches of the route where the new pipeline was installed underneath 4,000V cables supplying the National Grid. There were four such stretches in all, ranging between 70 and 90m in length. The drilling was carried out to a similar depth to enable the pipeline to travel 115m below a wooded copse and below a Bronze Age burial site, which was identified by the archaeologist overseeing the project as too sensitive for an open cut installation. The project also required DD for four road crossings and to pass under Goring & Streatley Golf Course, which had to remain fully operational throughout the installation. Thatcher continues, "Any damage to the fairways or greens at the golf course was out of the question, so DD was the only solution. This section of the pipeline was also completed last as we had to avoid the period over the summer and early autumn when the golf course is busiest and hosts tournaments. "As a result, we could not get onto site here until the end of October – just as the weather took a turn for the worse – and the imperative was not how quickly we could install the pipe, but how little disruption we would cause in the process." Optimising assets Meeting future water demand is one of the key imperatives of AMP5 and making improvements to the infrastructure that maximise the value of existing WTW is both a cost efficient and environmentally sound approach. The new pipeline that runs between Woods Farm and the Gatox main is an excellent example of how this can be delivered in practice and how no-dig installation techniques can be employed to overcome all kinds of infrastructure and environmental challenges along the route. nnn Perspectives Contractor "The whole programme was designed to be as time and cost-efficient as possible. Simple steps like doing all the open-cut first then all the no-dig, rather than approaching the installation in a linear fashion, meant that we could minimise the amount of time required on site for the trencher and the Polyhorse, ensuring that equipment didn't sit idly on site at waiting to be needed again." Roger Thatcher, project manager, Optimise JV Client "A lack of connectivity to the mains network limited supply from the site to the local area and was preventing us from utilising Woods Farm WTW to its full abstraction capabilities. The new pipeline project is designed to remove this constraint on the network by linking the site to the Gatox main, which transfers water to Oxford and Swindon. "The south-east of England is seriously water-stressed, so we need to make the best use of all the water available to us and this scheme will optimise the Woods Farm WTW asset, helping to deliver better supply resilience to high demand locations." Andrew Popple, capital delivery manager, Thames Water Over 70% of the installation was delivered by open-cut technique Continuous pipe lengths are generated on site

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