The culvert rehabilitation project at Ballyogan Landfill in Dun Laoghaire, Ireland has been a technically complex job with a very good outcome.
A Strategic Improvement Plan (SIP) – prepared as a preamble to the final capping of the landfill – highlighted that a pair of 1350mm diameter river culverts were at risk of structural failure in the medium to long-term due to their location and age.
After careful consideration it was decided that refurbishment, rather than total replacement, would be the best option. The tender documents stated that methodologies which avoided the need for personnel to enter the culverts were preferred – and the subsequent review of tender proposals concluded that the most efficient and cost-effective method of carrying out the “non-entry” refurbishment was to use cured-in-place pipe (CIPP) technology.
RPS – appointed by Dun Laoghaire Rathdown County Council as consulting engineers for the landfill rehabilitation – recommended CIPP technology due to the difficult site conditions and the need to protect fishery interests. The Ballyogan Stream, which runs through the culverts, is a significant fish-breeding asset, monitored by Ireland’s Eastern Fisheries Board.
The culverts extend through the body of the landfill site and therefore the refurbishment required two installations of CIPP lining – each around 270 metres long. Temporary roads were needed to facilitate vehicular access to the culverts – and because of the close proximity of overhead power lines, cranes could not be used. Due to an 8-metre height difference between the adjacent ground and the culverts, complex scaffolding was erected to feed the liners into the inlets. This scaffolding was designed to facilitate the consecutive lining of both culverts.
The work, which was carried out last year, was scheduled to start in August and finish in September. Actual installation took just three days for each culvert – including the hot water curing of the liners. Cora Plant, RPS senior civil engineering consultant said ”Using CIPP technology for the culvert refurbishment avoided health and safety risks associated with working in a river course which was liable to flash-flood. It also enabled a significantly shorter timescale for the work.“
Cormac Bradley RPS construction manager agreed that CIPP was a time-efficient method of carrying out the work – ”The project ran exceptionally well. It was completed within three weeks – from site establishment to site closure.“
It was extensively covered in the March 2010 issue of the trade journal WET News – and has also featured in the NATM magazine. A paper on the project has been presented at recent seminars – Engineers Ireland (in Dublin) and United Kingdom Society for Trenchless Technology (in Belfast and Dublin) – thus generating excellent promotion of RPS’ engineering expertise.
Contacts:
Cora Plant T: +353 (0) 1 488 2900
E: cora.plant@rpsgroup.com
Cormac Bradley T: +353 (0) 1 488 2900
E: cormac.bradley@rpsgroup.com
Image Notes:
Main Image and Thumbnail Image:
Overall site set-up showing scaffolding system to support the drawing in of the liner to the culverts. The liner is drawn out of a refrigerated truck on conveyor belts and then drops vertically (using gravity) before being drawn into the culvert. Once in place hot water is pumped into the culverts causing the resin in the liner to "go off" resulting in a fibre-glass like finish to the liner. A conveyor system was used due to the immediate proximity of a 220kV line preventing the use of cranes on site.
Second Image:
An overall view of the site set-up showing the height differential between the site set-up and the culverts below. The adjacent electricity substation (in the left of the photograph) influenced the choice of remedial methodolgy (deep excavations would have been needed to carry out conventional culvert replacement).