Water & Wastewater Treatment

PROJECT FOCUS 12 Water & Wastewater Treatment February 2014 W ith most large-scale construction projects there is always a significant amount of advance or enabling works that need to be undertaken either prior to or during the main construction operation. Crossrail, the major cross-London rail tunnel project, is no different. One such project is the Crossrail Contract C233 – Enabling/Advanced Works scheme which included mains diversion around the North Woolwich Portal and Victoria Dock Portal to enable the main tunnelling works. With Crossrail and the company's consulting engineer Hyder Consulting as the client, J Murphy & Sons was awarded the main contract for completion of this part of the works. This included a requirement to ensure that all existing and new sewer networks were structurally lined to protect them from potential damage during nearby construction works on the main portal. In addition, the linings had to ensure that new and existing pipelines were protected against aggressive effluents. Flow samples previously taken from the existing sewers showed that aggressive effluents flowed through the pipes, which meant that any linings used would need to use a site-specific vinylester resin to ensure the liners could withstand these aggressive flows. The lining contract for the locations on Factory Road and Albert Road were ultimately awarded to specialist subcontractor McAllister Bros. Liners of 1,220mm diameter were required at all lining locations on the trunk main. Various branch lines off this trunk main, with diameters from 225mm up to 900mm, also required lining. Ground and working conditions for these sections were difficult because both Murphy and McAllister were scheduled to carry out works at the same time in the same space. To overcome the lack of useable space, McAllister Bros used its UV-cure lining system which requires a small footprint in which to operate. This ensured both contractors could work together efficiently. Another difficulty with the site, again due to both contractors working in the same space, was that on some of the sections where lining was required there were deep excavations around the lining launch manhole with exposed existing services such as gas mains, water pipes and electricity conduits and cables. McAllister constructed platforms and slides that enabled the lining crew to install the liner without damaging the exposed service pipes. Despite these restrictions, the lining works were completed with only one lane closure and in a short space of time. This was due to the fast and efficient UV Blue Tec System that McAllister Bros used to cure the liners. Each section of 1,220mm liner was installed in a single 12 to15 hour shift. Elliptical shape WRc-approved GFRP liners for the works were supplied by German manufacturer Impreg. One section of sewer on the project required a lining that was a 1,650mm x 1,000mm elliptical shape. This is believed to be one of the largest liners installed to date anywhere in the world using UV technology and is certainly the largest in terms of distance from crown to invert for a UV-cured liner. To complete this elliptical installation successfully, McAllister's powerful Blue Tec UV light-train required use of a special wheel-set to ensure it was kept centrally in the pipe, providing an even distribution of UV light and heat to fully cure the liner. Lining operations Flow samples of effluent were taken so that the liner manufacturer could produce a bespoke vinylester (VE) resin to withstand the aggressive effluents, a task that was completed very successfully. Soil-type samples were also taken and the level of the water table was established to give McAllister an indication of the ground conditions, to ensure that the liner design took account of all possible future variations in condition that it could encounter. The condition of the existing pipe was also assessed to determine the structural design of the liner. All these parameters were used to produce a static calculation for each liner section. This calculation gave the contractor the required wall thickness for the liner. In the event, the liner design showed that the Impreg UV cured liners using VE resin required a 9mm wall thickness. The liners were produced in Germany and shipped to site in sealed boxes to Working alongside other operatives in a very restricted space made a sewer-lining project, which was part of the Crossrail enabling works, especially challenging. On behalf of McAllister Bros, Ian Clarke explains Tight fit for Crossrail UV-cured sewers The UV light-train curing the large elliptical liner. Working in the same space as the main contractor and within existing services made access to site difficult. A 1,220 mm diameter liner delivered to site in a box weighing 8t. PROJECT FOCUS 13 February 2014 Water & Wastewater Treatment protect them from sunlight. They can be stored for up to six months, giving the contractor a lot of flexibility on site. The lining works were completed within a seven-week programme between April and June 2012. Due to the requirement that some liners needed to contain the peroxide component in the resin mix and a lack of suitable storage space onsite, McAllister was required to stagger liner delivery as the peroxide liners needed to be transported at temperatures of between 5 and 25°C. As the work requiring these liners was to be completed during a hot weather period in May, with temperatures potentially in excess of 25°C, there was a risk of liner damage. Therefore the liners were transported to site in refrigerated trucks and installed soon after arrival. Each liner was completed in a single shift. For the bigger diameter or longer length sections as previously mentioned shifts of 12-15 hours were required. On completing these long shifts the crew was given a 'rest day' to recover before moving to the next liner site. Site difficulties Thames Water, owner of the sewer pipes being lined, had categorised all the sewers as 'Category C', which meant that the sewer effluent is aggressive and harmful to persons. It also meant that the atmosphere within the sewer/manhole chamber was dangerous. To overcome this McAllister's crews were required to use full body PPE and use full BA (breathing apparatus) during any works in the manholes or pipelines. Whilst all these works were being undertaken, the sewer flows needed to be bypassed around the work site. McAllister worked closely with Thames to find the most suitable method of diverting flows from a 1,220mm sewer with only limited space for equipment such as pumps and hoses. Existing flows were diverted into nearby Victorian culvert which was used as a channel to divert the flows past the works. These flows were diverted as far down as the next sewer treatment works, where the Thames Water operatives had to deal with this new entrance of flow. This bypass operation was closely monitored for the duration of the works to ensure all trade effluents from nearby factories could be dealt with. With a view to minimising the impact of the works on the local area as much as possible and with the works being adjacent to a residential area with some businesses that would be affected by the works, J Murphy & Sons informed all concerned of the works taking place. nnn Perspectives Contractor "McAllister assisted Thames Water Utilities with developing a liner that would meet all the required design requirements and elevate all concerns. From the outset McAllister has demonstrated the company's expertise in this field which benefited the project considerably. McAllister approached the project with a very positive attitude, a high level of enthusiasm and professionalism. McAllister has also worked closely with J Murphy & Sons with the successful completion of this section of the project. "The company had a very tight programme to work with and successfully kept within its programme. J Murphy & Sons was well informed of the progress and sequence of works at all times. "McAllister was very efficient and professional at all times and the company's work force has always come across as courteous to the general public, J Murphy & Sons and to the Crossrail teams. McAllister's works were executed to the highest level of quality and safety with confidence and accuracy at all times and J Murphy & Sons is very satisfied with the completed lining works." Joe Carroll, construction manager, J Murphy & Sons Specialist subcontractor "With this project we easily overcame any challenges and installed one of the largest diameter UV-cured liners to date anywhere in the world. Working together with Crossrail, Thames Water and J Murphy & Sons on this project was very enjoyable and it further strengthened our market presence in the region." Leo McAllister, director, McAllister Bros Innovations The works were carried out in a small area with both J Murphy & Sons and McAllister Bros crews working in close proximity. Existing services were exposed and the liner crew could not park its UV unit and liner boxes close to the manhole. The liner box used for most of the 1,220mm liners weighed in excess of 7t, with the largest box weighing over 8t.The liner boxes were required to winch the liner through the sewer as part of the installation process. To overcome this difficulty, McAllister constructed a number of platforms and slides to allow the liner to be slowly winched in place with the use of a 10t cable winch. The liner was lifted out of the box using a sling attached to a crane. Specially constructed platforms and slides enabled liner installation to be achieved within the confined space available. There was no need to remove the manhole frame (biscuit) as the liner easily folded to fit through a 600mm manhole frame during installation.

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