Last year, Aarsleff Ground Engineering were contracted as the Specialist Ground Engineering and Piling Contractor by Barhale and North Midlands Construction, the main contractor to work on the Raw Water Project in Stourport, England.
The Birmingham Resilience Scheme, worth an estimated £300 Million, is one of Severn Trent’s biggest ever infrastructure projects, specifically to develop an alternative water supply for Birmingham to complement the Elan Valley Aqueduct (EVA). The original aqueduct was built between 1893 and 1904. Fast forward over 100 years and the aqueduct still provides drinking water from the Elan Valley to Severn Trent’s customers in Birmingham. The aqueduct transports high-quality water entirely by gravity. Having supplied water for over 100 years, the aqueduct is beginning to tire in three key locations and offline replacements are necessary. Aarsleff’s work facilitated a new abstraction point and pumping station on the River Severn, at Lickhill Quarry near Stourport, to which water will then be pumped along a new 25km pipeline, through pipes with a 1.0m diameter, to Frankley Water Treatment Works.
Aarsleff’s sheet piling works allowed a dry working area for their supply chain partner J Murphy Group to construct the secant piling to the intake structure. Sheet piles were then subsequently removed, and the entire structure was submerged to not be visible. Water was taken from the River Severn which will provide a new source for the aqueduct, while maintenance takes place on the original EVA (Which Aarsleff Ground Engineering are also involved). When the resilience plan is in operation, the city of Birmingham will be drawing water from at least four sources, rather than just one. Aarsleff installed a bespoke temporary sheet piled cofferdam which included 200 No. AZ26 steel sheet piles (section modulus 2600cm3/m of max length 8.0m), with an integral enhanced toe support system comprising of 53 No. 254/254/132 S355 JO H-Section piles complete with prefabricated box section connection detailing at 1.26m centre to centre to provide a vertical guide for H-Section piles. This was required due to the very shallow underlying bedrock, which only allows for a limited sheet pile penetration, which was insufficient toe depth or embedment to withstand rotational forces. Access was provided by a temporary access works platform, allowing safe working over water. Aarsleff employed a high-frequency vibratory hammer and an impact hammer to drive its piles, using panel driving techniques. Aarsleff employed a 110-tonne capacity mobile crane operating at a maximum 25m radius to unload and handle piles and hammers.
The scheme was a technically challenging scheme to be involved with requiring a lateral thinking approach to resolving the challenging problems. Early contractor engagement between J Murphy and Aarsleff Ground Engineering identified significant technical deficiencies in the early engineering proposals for the temporary works cofferdam. Whilst reasonable assumptions had been taken, by the client Severn Trent Water and their engineers, it was quickly apparent that construction tolerances and environmental considerations had been overlooked in the preliminary details at tender stage.
Aarsleff took on the design responsibility and interface with structural propping designs by Barhale. Aside from delivering the project on time and within budget, Aarsleff were also able to reduce risk and environmental damage. Risk reduction through the application of practical construction methodology, and Reduction in Environmental impact, as the original scheme involved drilling underwater and spoil flushed directly into the watercourse. Steel sheet piles were also recovered for re-use making this element of the scheme carbon neutral. Aarsleff took the technical challenge and applied sense and reason to develop a practical, constructible and engineered solution, which benefitted all parties for the Environmental, Commercial and Safety aspects. Meeting a tight construction programme at the front end of a long complex scheme gave Aarsleff great satisfaction.