Pipeline project comes into focus

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.

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.