Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | APRIL 2014 | 13 Gurney (KMG). As a significant part of the planned works was to use trench- less lining techniques, these works were subcontracted to rehabilitation specialist contractor Matt Durbin As- sociates. The £8M project will add a structural lining within the aqueduct in order to strengthen it, extend its functional life and improve the flow of water through the structure. The work is designed to be confined to small areas around the shaƒs that give access to the aqueduct and is largely confined to the Litton Area and in East Harptree (located at Harptree Coombe) as well as West Harptree and Chew Stoke. Phased construction Whilst the majority of the 19km-long aqueduct runs underground at depths of up to 40m through predominantly sandstone and limestone strata, it does run on surface at Harptree Coombe, crossing Watery Lane near Winford and finally as a backdrop to the village of Winford itself. The whole rehabilitation programme was planned to be completed over three years in 2012, 2013 and a final stage in 2016. It involves using a variety of techniques including: • The installation of glass- reinforced plastic (GRP) liners • Concrete spray lining • Grouting of the existing tunnel Access sha s In order to provide adequate access to the aqueduct, it was also necessary to construct three new shaƒs onto the structure, in Litton, East Harptree and near Winford. These were successfully completed in 2012. In addition to the lining works, Bristol Water is also taking the opportunity to improve existing facilities on the Line of Works system to help operate and maintain the network more safely and efficiently. The techniques listed above were ultimately chosen aƒer careful consideration of the rehabilitation available on the market. The depths and access restrictions associated with the refurbishment works prohibited cost effective use of remote refurbishment techniques and this led to the selection of the specialist man-entry techniques throughout the aqueduct. Apart from the new shaƒs, access from the surface was generally restricted to the use of existing A section of the overland aqueduct route • Challenges 1 ● Given the location of the various works and the access requirements there were a number of logistical problems associated with the pro- jects undertaken to date. These included dimen- sional constraints within the aqueduct with limited cross-section dimension. This was combined with depth and distance between surface access points, 620m being the longest, which restricted effective pumping distances for the micro- concrete spraymix, par- ticularly for the wet spray technique. Although dry spray tech- niques overcame this specific difficulty with improved pumping per- formance, the extremely confined access condi- tions within the aqueduct substantially increased non-productive opera- tional time such as clear- ance of excess material and surface finishing. ● Further to this, all access sha s were located on agricultural land and one section of work was to be carried out within a Sites of Special Scientific Interest (SSSI) area at Harptree Coombe. This meant that close liaison with landowners and all other interested parties had to be maintained and supported at all times. • Collaboration ● Due to the location and critical nature of these works, the contractors collaborated to organise a mock emergency rescue scenario, involving the specialist Hazard Area Response Team (HART) and Urban Search & Rescue (USAR) team from the emergency services. This involved extraction of a casualty from a depth of 14m and some 100m along the aqueduct, using specialist rope-access techniques. ● The trial run created good communication between all parties and provided the emergency services with an excellent chance to sharpen their skills in a live situation. With health and safety being at the forefront throughout, no accidents or incidents have occurred during the project.

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