Water & Wastewater Treatment

14 | APRIL 2014 | WWT | www.wwtonline.co.uk Project focus: Bristol aqueduct lining Top: Installing HDPE invert sections in 2013 Bottom: Emergency services during the mock rescue exercise shas, which were typically 1,200mm diameter, with many of the deep shas only being 900mm in diameter. The works undertaken in 2012 involved the installation and grout- ing into position of some 1,200m of GRP segmental lining. All preparatory works, such as cleaning and jetting, was carried out manually. The grouting operation to complete the lining works around the liner seg- ments was completed with a Colmono CX410 high shear colloidal mixer. The GRP liner segments used for the 2012 works were provided by Stanton Bonna, with the grout product being procured from Tarmac Pozament and Readers respectively. The 2012 works were completed over a 12-week con- tract duration commencing 7 June. The rehabilitation works carried out in 2013 initially involved the placement of HDPE invert pieces into the aqueduct. This was followed by the installation of stainless steel mesh around the crown of the tube onto which was sprayed a final surface treatment of 40 Newton micro- concrete. Spray techniques Both wet/dry spray techniques were used depending on the surface condi- tion prevailing at the location of the installation. All of this was followed by interstitial/extrados grouting of the refurbished structure. The HDPE invert units were supplied by Asset International, whilst the Spraycrete 40 (wet) and Spraycrete 40 (dry) was supplied by Readers. The stainless steel mesh was sourced from Dyers Metal & Mesh with the final grout being supplied by both Readers and Tarmac Pozament. The 2013 works were completed over a 14-week contract duration commencing 2 July. Installation obstacles Given the location of the various works and the access requirements there were a number of logistical problems associated with the projects undertaken to date. These included: dimensional constraints within the aqueduct, its limited cross-section dimension and the depth and distance between surface access points. Further, the access shas were located on agricultural land and one section of work was to be carried out at a Site of Special Scientific Interest. Due to the critical nature of these works, the contractors organised an emergency rescue scenario. To date, with all but the final phase completed, there have been no incidents to report. • Perspectives Main contractor "MDA mobilised efficiently and maintained resources throughout to finish both phases of the contract on programme. Its workforce operated consistently with a strong health and safety culture. "Engineering solutions were offered and implemented to overcome the isolation and infiltration challenges that arose on several of the sections. They were a very professional team." Mike Barron, project manager, Kier May Gurney Specialist lining contractor "I was extremely proud to be able to complete this challenging and critical project within budget and to the limited timescales on behalf of MG/Kier, with all parties working in collaboration throughout the project to enable successful completion to the satisfaction of Bristol Water. It was also a great privilege to be involved in renovation of a structure that is testament to the highly skilled men that were involved in its original construction." Matt Durbin, managing director, Matt Durbin Associates • Challenges 2 ● Protective environmental measures were required when working within Harptree Coombe SSSI, where pollution control measures were required of the very sensitive watercourse, as well as protection of trees and their roots. The main contractor Kier/ MG provided the work teams with access to each sha by either temporary road surface or designated routes that were pre- agreed with landowners. Site vehicles were fitted with low-impact ground- pressure tyres to reduce surface damage, which was essential in 2012 due to the very wet summer. Deliveries were scheduled to be outside of peak times to minimise any disruption to the local residents. Industry leading screenings removal technology No requirement for holding tanks or buffering Minimum operator intervention Minimum civils requirement CDEnviro Ltd T: +44 28 8676 7900 E: info@cdenviro.com W: cdenviro.com S:MAX Visit us at IFAT Booth A1.113/212

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