Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/374689
16 WET NEWS SEPTEMBER 2014 Different parts of the aqueduct showed differing dimensions ONSITE AQUEDUCT REFURBISHMENT GRP sectional liners were used in some parts of the aqueduct in 2012 (left) and HDPE invert sections were installed last year (below) In order to provide adequate access to the aqueduct it was also necessary to construct three new shas onto the structure, in Litton, East Harptree and near Winford. These were success- fully completed in 2012. The techniques listed above were ultimately chosen aer 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 newly con- structed shas, access from the surface was generally restricted to the use of existing 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 grouting 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 segments 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 respec- tively. The 2012 works were com- pleted over a 12-week contract during that year›s summer. The rehabilitation works car- ried 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 sur- face treatment of 40 Newton micro-concrete. Both wet/dry spray techniques were utilised depending on the surface condi- tion prevailing at the location of the installation. All of this was followed by interstitial / extra- dos 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 stain- less steel mesh was sourced from Dyers Metal and Mesh with the final grout being supplied by both Readers and Tarmac Poza- ment. The 2013 works were com- pleted over a 14-week contract duration commencing last sum- mer. Given the location of the various works and the access requirements there were a num- ber of logistical problems asso- ciated with the projects under- taken to date. These included dimensional constraints within the aqueduct. The limited cross section dimension, combined with depth and distance between surface access points, 620m being the longest, restricted effective pumping distances for the micro-concrete spraymix, particularly for the wet spray technique. Although dry spray techniques overcame this spe- cific difficulty with improved pumping performance, the extremely confined access con- ditions within the aqueduct substantially increased non- productive operational time such as clearance of excess material, and surface finishing. Further to this, all access shas were located on agricul- tural land and one section of work was to be carried out within a 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. To date with all but the final phase completed there have been no incidents to report. Protective environmental measures were required when working within Harptree Coombe SSSI, where pollution control measures were required of the very sensitive water- course, 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 desig- nated 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. Rescue scenario Due to the location and critical nature of these hazardous works, the contractors worked in collaboration to organise an emergency rescue scenario involving the specialist USAR and HART teams from the emer- gency services, this involved extraction of a casualty (from a depth of 14m) from 100m within the aqueduct using specialist rope access techniques. This created good communication within all parties also providing the Emergency Services with a chance to sharpen their skills within a live situation. With Health & Safety being at the forefront throughout, no acci- dents / incidents have occurred throughout the project. For main contractor Kier MG, Mike Barron comments: "MDA mobilised efficiently and main- tained resources throughout to finish both phases of the con- tract on programme. Its work- force operated consistently with a strong health and safety cul- ture. Engineering solutions were offered and implemented to overcome the isolation and infil- tration challenges that arose on several of the sections. They were a very professional team." Matt Durbin, of Matt Durbin Associates, the project's special- ist lining contractor, adds: "I was extremely proud to be able to complete this challenging and critical project within budget and to the limited time- scales on behalf of Kier May Gurney, with all parties working in collaboration throughout the project to enable successful completion to the satisfaction of Bristol Water. " n The contractors worked in collaboration to organise an emergency rescue scenario involving the specialist USAR and HART teams from the emergency services