Articles & Case Studies

PE pipe contributes to Norwich water boost

Posted: Monday 8th November 2010

A project delivered by the @one Alliance for Anglian Water to increase supply capability to Norwich has installed almost 8km of polyethylene pipe from GPS PE Pipe Systems, using microtunnelling technology in the process.

The Norwich Resilience scheme benefited from the faster installation and commissioning offered by PE pipe systems in comparison with other materials. This enabled the work to be completed within 14 months, providing the area with the potential to double its drinking water flow rate and putting safeguards in place against possible flood contamination, or shortages.

The new, 560mm diameter ‘resilience’ pipelines connect chalk aquifer boreholes at nearby Costessey with the Heigham Water Treatment Works and the city’s clean water supply network. Pipe provided by GPS comprised 3.15km of SDR21 8bar black PE for abstracted raw water and 4.55km of SDR17 10bar blue pipe for the treated supply line.

As part of the @one Alliance, Balfour Beatty Utility Solutions constructed the pipelines largely by butt fusion of 12m pipe lengths. Several GPS SlimFlanges were employed on the potable water main. These stainless steel flange adaptors are strong and compact, allowing for an unrestricted flow of water without the need to upsize any pumps or valves to which they connect.

Anglian Water was greatly concerned to minimise the environmental impact of the project, in terms of the effects of increased water abstraction and disruption due to the pipeline installation. Part of the project also takes in a conservation area. Engineers used open-cut working and trenchless installation methods, choosing microtunnelling to drive the pipes underneath the River Wensum, at two crossing points. The microtunnelling operation was completed by Barhale, another member of the @one Alliance. The work was conducted between shafts, below ground, such that disruption on the surface was minimal. Once installed, all pipe remained completely out of sight, with no impact on other infrastructure, wildlife or landscape.

At the crossing depth of around 9m, the ground consisted of structureless chalk. In these difficult ground conditions, microtunnelling was chosen in preference to directional drilling or auger boring. Working from 5m diameter by 14m deep launch and reception shafts, the project team successfully created 74m and 50m crossings to take the GPS pipe, through steel casings, under the river. Pipe was pre-cut into 3m lengths suitable for lowering into the launch shafts and welded as the installation progressed.

The project team considered several advantages of PE pipe systems, when selecting the GPS product rather than ductile iron pipes. A major advantage was the reduced lifetime cost of the whole project, taking into account material costs, maintenance and the efficiencies of installing PE. By employing SDR21 pipe, instead of thicker-walled SDR17, the pressure rating was preserved with a cost saving of around 20%. Similarly choosing SDR21 and SDR17 in place of SDR11 produced savings of 45% and 30%, respectively. Another key issue was the relative speed of commissioning the PE system, with trouble-free chlorination and lower test pressure. Flexibility and ease of installation also stood in favour of PE in this application.

The project increases the resilience of Norwich’s water supply by reducing its dependence on a single, large WTW at Heigham, in the event of an incident affecting supply. The scheme went into supply in August 2010.

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