Client

Network Rail

Value

£528K

Location

West Lothian

THE PROJECT

Avon Viaduct, UB070/047, crosses the River Avon and is located on the Edinburgh to Glasgow Mainline at 28 miles and 122 yards. The bridge is a Grade A listed 23 span masonry arch viaduct which was constructed in 1838. The substructure comprises of masonry wingwalls and orthogonal masonry abutment walls with intermediate masonry piers.

Following a scour report carried out in October 2018 it placed the piers located within the river at high risk of scour with a EX2502 score of 18.10. As a result of this a detailed design was carried out which involved a concrete skirt and masonry repairs to the piers in order to bring the scour risk down to a score of 10 (low risk).

This was a challenging project due to the works being carried out within the water course in autumn when rainfall is typically high as well as the essential environmental considerations due to working in the river.

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The scope of the project was to design and implement the following works:

  • Provide a solution to repair and prevent further scour to the bridge substructure.
  • Develop a temporary works system to create a ‘dry’ working area in two separate phases whilst still maintaining the flow of the river to satisfy SEPA and local fisheries conditions.
  • • Carry out fish rescue prior to each phase of works.
  • Excavation at piers down to existing bedrock and determine any undermining of the existing piers.
  • Drill and fix dowels and steel mesh to the existing piers and then pour a concrete ‘skirt’ around the pier.
  • Carry out masonry repairs to the existing piers and adjacent retaining wall.
  • Installation of concrete bags to the underside of the gabion baskets to repair current scour and prevent any future scour.

Our project team worked in close collaboration with the Scottish Environment Protection Agency (SEPA) and Forth River Trust (local fisheries) in the planning, construction and handover of the Project to ensure there were no adverse effects on the condition of the river and its habitat. Due to works being carried out in autumn and continuing into the fish spawning season continuous dialogue was maintained with the Forth River Trust and the site had a designated Environmental Clerk of Works (ECoW) who visited site weekly as a minimum during the fish spawning season.

We also worked closely with our Client (Network Rail) in agreeing the relevant land accesses to allow the works to be taken on. Our project team maintained contact with the landowner and local residents throughout the project to ensure there was minimal disruption to them during works.

The project was able to celebrate success and demonstrated best practice within the following areas:

  • Early consultation with affected local land owner and local residents in close proximity of the works resulted in good community relations.
  • Developing a relationship and keeping in constant contact with SEPA representative and Forth Rivers Trust allowed the works to be carried out throughout October when typically works within the water are not possible due to fish spawning season.
  • During the design phase of the project an accurate survey of the existing pier foundations was not possible due to existing rip rap around the piers. Therefore, a detailed design was carried out to cover both possible outcomes of the survey. Design engineer was present on site at all times when excavation to foundation level was carried out which allowed for an instant decision to be made on the solution to be taken on site this preventing any delays to the programme.

Works completed
two weeks
ahead of schedule

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