Pipeline project comes into focus

The £125M West East Link Main (WELM) pipeline scheme for United Utilities is one of the most ambitious pipeline projects that the North-west of England has ever seen. Maurice Corridan, project director at J Murphy & Sons, gives the low-down on the project.

Contractor J Murphy & Sons (Murphy) is building a 54.5km, 1,200mm diameter welded steel pipeline to carry potable water bi-directionally from Prescot Reservoir near St Helens, to Woodgate Hill Reservoir in Bury under an NEC 3 Option C design and construct contract. The system will be able to transfer water via gravity from Woodgate Hill to Prescot and pump water back again through this new dedicated regional trunk main.

The contract was awarded to Murphy in December 2008 and the main project has been a collaboration between United Utilities, Murphy, Jacobs Engineering, Montgomery Watson Harza (MWH), Atkins and Nomenca. Once completed in 2011, the pipeline will be able to move 100M l/day to help safeguard supply for the region’s 7M customers, and provide more flexibility in the system in the future in times of drought and to allow maintenance on other major pipelines in the region, not least the inspection, cleaning and remedial works on the large aqueducts serving Liverpool and Manchester.

The scale of the project and extent of the route presents many engineering challenges. These include varying ground conditions, from rock to peat, redundant mine works, ecological issues, the terrain, traffic management and the timescales required to complete the works.

There are 44 road crossings including the M6, M61, M66 and the East Lancs Road (A580) at three locations. Major rivers including the Irwell and Roch and the Bridgewater Canal had to be traversed, as did six railways lines including the West Coast mainline, Manchester to Bolton, Bury to Manchester and the Metrolink Tram line.

Murphy is using a variety of construction techniques including standard open cut trench as well as trenchless techniques utilising augerbores, microtunnels of 1,500 and 1,800mm diameter, and a pipe bridge over the River Roch. Many of the crossings involve the sinking of segmental shafts to depths of up to 30m.

The original design included the scope for 15 tunnels along the route, but this has now increased to 29, culminating in 5.2km of tunnels on the scheme. In a normal pipeline scheme you may get one or two tunnelled crossings, but to have 29 tunnels along the route in a single contract is quite a feat of engineering to manage and deliver them within the timeframe.

The route of the pipeline involves liaison with more than 300 landowners, planners and eight separate borough councils – Knowsley, St Helens, Wigan, Warrington, Salford, Bolton, Bury and Rochdale, as well as bodies such as the Environment Agency, English Nature, Network Rail and the Highways Agency.

Sections of the pipeline are also being laid through residential areas, industrial and retail locations, school grounds, public parks playgrounds and five golf courses. Consequently regular and close liaison with stakeholders has been an essential part of the delivery process.

Along the route Murphy has encountered wide ranging ground conditions including contaminated ground, rock and 1.5 km of peat.

Detailed site investigation in the old mining areas around St Helens and Bury highlighted the need to carry out extensive probing and grouting prior to the commencement of the mainline works. Ecological constraints have included the presence of protected species such as great crested newts, badgers, water voles, bats and invasive species like Japanese knotweed and Himalayan balsam.

Since the Woodgate Hill reservoir is approximately 65m higher than Prescot reservoir, control of the gravity flows east to west to Prescot is achieved by two slotted needle valves. To transfer it west to east, two new huge 5m tall pumps at Prescot pumping station will deliver 90Md/d. A new 11kv substation is being built to handle the additional power requirements. For the pipeline to flow effectively it must be laid to a precise gradient of 1:300.

Murphy’s excavators are fitted with laser levelling devices to ensure they are kept at the correct depth and gradient all the way along the trench. Flow meters at both end of the pipeline will monitor flows and potential leakage. Remotely controlled sensors along the route monitor pressure, and are capable of shutting the pipeline down if needed and pinpointing any leaks once operational.

As well as the challenges detailed previously which characterise the scheme, careful timing of the works also plays a huge part in minimising the environmental impact, and accommodating Mother Nature. Hedge removal and pre-construction works to open up the working corridor was carried out autumn and winter 2009 in advance of the bird nesting season, while the majority of the construction work is taking place this summer to take advantage of the longer days.

More than 25km of pipeline was planned to have been installed during 2009, but due to planning constraints, this did not take place, putting the onus on Murphy’s ability to lay the bulk of the pipeline during 2010.

At its peak the scheme had 450 construction personnel working on site. This has now been scaled down slightly to 380 personnel with six mainline pipe crews installing an average of 3km plus per week, two auger boring crews, four shaft sinking gangs and five tunnel boring machine (TBM) crews out on site.

At the end of July 2010 the WELM project had delivered a milestone of over 1,000,000 man-hours RIDDOR accident free and an accident frequency rate (AFR) now standing at 0.14. Cumulative man-hours worked on the WELM scheme up to end July 2010 were 1,386,065.

The bulk of the personnel are all directly employed by Murphy. However the services of three specialist tunnelling crews were used in specific locations – Active, Barhale and B&W – and three specialist sub-contractors for all the greens reinstatement at each of the five golf courses. Specialist M&E contractor Nomenca was employed to design, procure and install mechanical & electrical works at Prescot pumping station.

A recent milestone was the start of one of the longest tunnelling drives in the scheme which began at the end of July 2010. Using micro tunnelling techniques, we kicked off the 650m drive underneath the Metrolink line and into Springwater Park near Bury, which links Hollinhurst Road with Springwater Park at the top end of the pipeline route, culminating in Woodgate Hill service reservoir.

Around 10km of the pipeline route passes through Bury, including tunnels under the River Roch and the M66 motorway and the East Lancashire Railway. Hollinhurst Road is one of the few places where the pipeline is being laid in a residential road. Two houses were purchased and demolished and a deep shaft sunk on the site to provide the access point to lower the TBM into position.

In locations such as this, the working corridor has been reduced from the 40-50m wide that is the norm, to just 5m in places, adding to the pressure in terms of managing the logistics and impact of the works on the general public which requires well planned and effective traffic management.

Following the successful completion of the Springwater Park crossing, we moved our attention to the only section of the pipeline which will not be buried – a pipe bridge over the River Roch. Due to broken ground and fractured rock, the site was not considered suitable for tunnelling, and a pipe bridge alternative was agreed.

The 36m pipe bridge fabricated off site by Fussey Engineering was delivered to site in August 2010 and installed in one single section.

Large diameter, long distance aqueducts and pipelines do not occur in the UK very often, so there has been interest in the scheme from the local and national media as well as the industry as a whole. Given a whole host of challenges, not least the sheer scale of the tunnelling aspect, the WELM scheme is a fantastic feat of engineering, planning and project management and will provide a lasting legacy for the region.

More than 25km of the installed pipeline has already been tested, with pipeline testing and commissioning carrying on in 2011.

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