Rannoch & Ghaoir Viaducts
"A wearier looking desert a man never saw" were Robert Louis Stevenson's choice words to describe the unforgiving landscape of Rannoch Moor. Sitting at an altitude of over 1,000ft, the moor is a labyrinth of lochs, lochans, peat bogs, and streams. It is surrounded by the mountains of the Glen Coe national park that rise to over 3,000ft to the east and west and to over 2,000ft in the north. The moor, one of the last really wild environments in Great Britain is approximately 50 square miles across, and is intersected by the single track bi-directional West Highland line running from north to south through the centre of this barren landscape.
In April of this year, Network Rail commissioned the Bolton based principal contractor TI Protective Coatings to undertake the simultaneous refurbishment of two viaducts in this unforgiving environment.
The first of the two structures, Rannoch Viaduct, is located 300m beyond the north end of Rannoch Station. Each of its nine spans are supported upon masonry piers. The five span Garbh Ghaoir Viaduct, the second of the structures, spans the SSSI designated River Ghaoir, and is located 1.2km to the south of Rannoch Railway Station.
In order to reach both isolated structures over the treacherous, ever changing terrain, TI Protective Coatings laid over 2.5km of aluminum panels to create two roads which would allow their vehicles to traverse the moorland throughout the eight month project. This floating roadway overcame the first of many challenges which would require innovative approaches to ensure a successful outcome.
Once the roads were in place, construction could start on the three site compounds it would require to properly manage the project. The compounds were sited upon floating sections of aluminum paneling. These areas had to be strong enough to sustain the weight of the facilities, vehicles and materials which would be stored upon it, whilst ensuring they could spread the load across the moor to prevent subsidence of the entire compound.
Once the infrastructure was in place, TI Protective Coatings were able to begin the physical work of restoring both structures after months of planning. Prior to commencing grit blasting operations, both bridges would undergo a full encapsulation to contain the high volume of dust created during the blasting process. Once the existing coatings and corrosion had been completely removed, TI Protective Coatings were in a position to apply the first coat of paint.
TI Protective Coatings needed to ensure that the structures would be protected for a minimum of 25 years, and so the Network Rail RT98 approved M24/014 system was selected, supplied by leading paint manufacturers Leighs Paints. To ensure a high quality, cost effective service was delivered throughout, all coats of paint were applied by ICATS accredited Industrial Painters.
Both structures were alive with a mass of different tradesmen. While coatings were removed by grit blasters in one location, painters would be applying new coats in the next. In the completed sections steelwork repair operatives would be carrying out the vital replacement of corroded sections of the super-structure. Beneath the structure, masonry repair specialists worked upon replacing and re-pointing areas of the masonry piers and abutments, whilst specialist piling contractors carried out the replacement of the ballast retention walls either side of both structures gaining access with Road/Rail Vehicles.
Despite this, the project wasn’t without its challenges. The structures unique location combined with its age posed a conundrum for the scaffolding contractor. The usual slung scaffold was not suitable, and the alternative to build from the ground up was impossible due to the ground conditions in the beneath the structures.
The solution was to cantilever the scaffold between the two masonry piers either side of the span, so that loadings were distributed into the substructure. This allowed Bolton Northwest Scaffolding, a division of TI Protective Coatings, to erect an intricate three tier scaffold accessed via a 4 storey aluminium staircase. The scaffold would go on to be fully encapsulated, and provide a safe working environment within which the refurbishment could take place.
The significant number of steelwork repairs on both structures also proved challenging. All trackside walkways across the two structures required renewal over a distance of 560m. The existing timber walkway beams had to be safely extracted, then the top flange of the supporting girders were prepared and painted before a galvanized Eurogrid mesh panel was installed. All of this took place during midweek possessions.
Jason Worrall, Rail Project Manager for TI Protective Coatings comments: “These particular jobs required a lot of initial planning and forward thinking before any work could be undertaken. The unique environment in which these sites were situated posed many challenges, but I am pleased to say that all were overcome. These jobs are part of a long list on which we have worked with Network Rail and I believe that our work here has ensured that our relationship will continue into the foreseeable future.”
In total the TI Protective Coatings applied over 8,400 litres of paint to Rannoch and Garbh Ghaoir Viaducts, taking 8 months to complete - some four weeks ahead of schedule.
If you would like to speak to TI Protective Coatings about this, or any other project then please contact us directly on 01204 468 080.
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