A beacon project

A pipeline is being built, which will carry 20% of the UK's natural gas supply, to help cope with growing demand for gas. Remote locations have posed problems, writes Paul Stearnes

Until now, the UK has been self-sufficient in gas, thanks largely to abundant supplies from gas fields predominately in the North Sea. But offshore gas production is decreasing while demand for gas is rising. And analysis shows that the UK will become increasingly dependent on imported gas.

To meet the demand, two terminals to import liquefied natural gas are being constructed at Milford Haven in Pembrokeshire. National Grid has an obligation to connect this supply to the National Gas Transmission System. And Murphy Pipelines has been awarded a contract to construct a 107km-long section of the pipeline from Brecon to Tirley.

When completed, the new pipeline will have the capacity to carry 20% of the UK's natural gas supply. As such, the whole project is of vital strategic importance for the future of the UK economy.

STATS was contracted to provide specialist technical services to the project. Initially, this involved the design, procurement, management and supervision of the ground and groundwater investigation of the proposed route. It involved post-investigation analysis of the collected data, and the submission of appropriate recommendations on design, construction and the final choice of route.

The main ground investigation posed considerable challenges due to the often remote locations and the rugged terrain in the foothills of the Brecon Beacons. Because of the environmentally sensitive location, National Grid was especially concerned this phase of the work was carried out with minimal impact on the land, both during and after drilling.

A total of 221 boreholes have been drilled to date, with a further phase of investigation about to start. But this represents a relatively low frequency per kilometre and the STATS geophysics team, led by Dr George Tuckwell, developed
the concept of virtual trial pits to investigate the soil characteristics and rockhead profile.

A total of 17 locations were investigated using this technique, and check drilling at two locations confirmed the ability of the virtual trial pits to identify rockhead to an
accuracy of +/-50mm.

Project manager, Jon Bassett said: "The site-based team worked closely with the designers, construction crews and the quantity surveyors to develop new ways with which to make the borehole and laboratory test data timely, relevant and meaningful. One outcome of this was that the interpretative report has little text. And, as a result, the non-specialist members of the project team can easily identify potentially problematic areas."

The pipeline route will also cross an aquifer, six rivers and more than 30 ditches. And STATS has provided an assessment of the likely affects on surface groundwater resources, including flood risk assessments wherever the route crosses the flood plain.

The firm has also provided the scope of work for surface water monitoring to be carried out prior to, during and for four years post construction.

A mining and quarrying hazard assessment has been done to provide a basis for evaluating likely zones of influence from historic, current and planned mining, together with an assessment of potentially economic mineral reserves that could be mined in the future. A landslide hazard assessment has been done by STATS on the pipeline corridor for areas of potential slope instability.

Commenting on progress to date, STATS director Paul Stearns said: "This project has allowed STATS to use our full range of specialist technical services to assist Murphy Pipelines and National Grid to deliver the project to very tight time constraints.

"Our biggest challenge has been to find the resources to manage the project. And the unsung heroes have been the field engineers, who have worked unbelievably hard over many months to produce top-quality ground investigation data - without which the specialist expert reports could not have been produced."

Paul Stearns is director of STATS. For more information visit www.stats.co.uk

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