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Innovative solution wins Fleming Award
An innovative slope drainage system completed in 2004 by May Gurney Utility Services was awarded first place at the final of the 2005 Fleming Award for its geotechnical innovation and excellence.
The award went to the whole project team, and was presented at the ICE headquarters in London to representatives from Isle of Wight Council (client), High Point Rendel (consultant), and Van Oord and May Gurney (contractors).
The May Gurney site team comprised Steve Ashman (Site Agent), Tim Smith (Sub-Agent) and Adrian Wood (General Foreman).
Castlehaven is located on the southern most point of the Isle of Wight and has been under threat from coastal erosion and landslide reactivation.
It forms part of the Undercliff landslide system, one of the largest developed landslide systems in western Europe, which is approximately 12km in length and extends up to 1km inland from the coast. Coastal erosion, high groundwater levels and susceptible geology reactivated this landslide, putting properties and infrastructure valued at £18m at risk.
Extensive investigations by Isle of Wight Coastal Authority and consultants High Point Rendel confirmed the main landslide failure mechanisms as being recession of the sea cliffs due to marine erosion and reactivation of the landslide due to high groundwater levels.
May Gurney Utility Services, working as supply chain partner to Van Oord UK Ltd, constructed an innovative siphon drainage scheme to control the groundwater. The system comprised 35 electro-pneumatic pumps driven by compressed air and 116 gravity fed siphon wells installed within 151 deep drainage wells at depths of up to 25mbgl. A unique feature of the siphon pump is the automatic priming arrangement, and that there is no need for power. This is the first scheme in the UK where these techniques have been used to stabilise landslides.
Steve Ashman says: "The works were very challenging and involved the laying of 4800m of pipe at depths of up to five metres. The working space was very restricted and great care was taken to ensure the construction activity did not further mobilise the landslip areas. The well points were installed using rotary drilling and water flushing. With up to three rigs on site, each with a pair of six inch pumps and three settlement tanks, this proved to be a complex logistical task on its own - even before you considered all the other activities being undertaken."
A combined total depth of 325m of manhole sections were installed during the construction of this complex drainage scheme, as well as extensive carriageway works to upgrade the local road network. A monitoring system was installed and commissioned early in the contract to provide accurate data for ground water levels and slope movement. The monitoring system comprised a fully automatic weather station, two vertical inclinometers, and around 30 vibrating wire transducer that recorded the ground water levels on a hourly basis. This system is now adopted by the client for ongoing assessment.
A 550m length of revetment was also constructed, comprising two layers of 3-6 tonne rock armour delivered by barge, which was placed at the toe of the sea cliffs to arrest marine erosion.
The site is covered by numerous environmental designations including SAC, SSSI, AONB and Heritage Coast. It is within this environmentally sensitive setting that a unique engineering solution was sought to improve the stability of the developed landslide while mitigating the significant environmental impact.
The 52-week, £4.6m project commenced in October 2003 and was completed on time and on budget. The scheme was notable for the way in which environmental issues were managed and how an innovative design solution was implemented - and the way in which the various parties worked in partnership to give the residents of Castlehaven confidence and security.
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A sustainable approach
May Gurney's stated goal of 'Being the best' construction and support services company is accelerating its progress in working with customers to develop more sustainable ways of doing business.
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CIWM Conference 2008
10-13 June
Torbay, Devon
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2007 - an award-winning year more >
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