B863 Invercoe Bridge Replacement
Background and Existing Site Information
The site is located at Invercoe Bridge, where it spans the River Coe. The bridge lies on the B863 Glencoe Village to Kinlochleven road. The River Coe is tidal at this location.
The existing bridge is a four-span reinforced concrete structure originally built in 1930. The bridge was showing serious structural deterioration to the main elements of the structure. Whilst there are no signs of structural distress, this deterioration reduces the strength and durability of the supports.
Due to the poor condition of the bridge, it was restricted to one-way traffic by the use of 2 lengths of MASS barrier.
As a result, the bridge was identified by The Highland Council as a high priority for replacement.
A preliminary study was carried out by The Highland Council, examining the various options for the new bridge. It was concluded that an online replacement using two 30m spans with a central support was the preferred option.
A temporary bridge (single lane, controlled with traffic lights) will be installed downstream of the existing bridge to allow continued access during construction works.
The project had a number of environmental factors to consider from the outset.
Following various fish surveys and consultation with the Lochaber District Salmon Board & District Fisheries Trust, it was concluded that construction works within the water should only take place between December and March (inclusive) to avoid disturbing the migrating salmon in the river.
The bridge crosses the tidal reach of the River Coe, therefore a Marine Licence was required to construct the bridge.
The principal contractor for the project would have to consider the above when finalising programme and methodology for the works.
Following a competitive tender via Public Scotland, The Highland Council awarded the Invercoe Bridge Replacement Project to Story Contracting in November 2021 with a total contract value of £5.5million.
The overall duration of the project was set at 73 weeks.
The client set out the following key milestones to comply with the approved Marine Licence:
- Completion of 1st phase in the river – 14/04/22
- Completion of 2nd phase in the river – 31/03/23
Story Contracting commenced on site on 13th December 2021 and are scheduled to be complete by 8th May 2023.
Temporary Bridge Design Solution
Story Contracting engaged with Janson Bridging UK Ltd. to provide technical support during the tender process.
A number of options (short span or long span) for the temporary bridge were considered during the tender period. Following a technical and commercial evaluation of all options to ensure compliance with client works information, the proposed solution was to install a 75m long temporary bridge with central support.
The main benefits of this option were as follows:
- Minimise environmental interface with tidal River Coe
- Reduce earthworks requirements on north side by having temporary abutment within existing embankment
- Reduce earthworks on south side by having south abutment set back from existing river channel
Following main contract award in November 2021, Story Contracting awarded Janson Bridging UK Ltd. the subcontract package for the design, supply and installation of the temporary bridge.
With the extremely tight timescales for achieving the 1st key milestone, Janson Bridges immediately commenced the detailed design for the temporary bridge. Story Contracting also appointed MHB consultants to undertake the detailed design of the temporary bridge substructure. Following a series of collaborative design workshops with all parties, the design was submitted to The Highland Council in late December 2021 and was subsequently approved early January 2022.
Temporary Bridge Installation
Story Contracting completed the construction of the temporary bridge substructure by the end of January 2022 in preparation for the temporary bridge delivery and installation by Janson Bridging UK Ltd.
Due to the geographical location, the pre planning of deliveries and installation required meticulous planning with the Janson Bridging team.
The original methodology at tender stage was the temporary bridge to be installed by 500t crane from 2 set up positions. One from the south abutment of the temporary diversion road and the other from the north abutment adjacent to the Invercoe Caravan Park. Following site investigation works by Story Contracting, it was determined that the existing bridge had insufficient capacity for the 500t crane to cross over. As a result a larger crane lifting from the south abutment side would be required for the installation.
Janson Bridging engaged with local crane supplier Global Port Services to determine the new craneage requirements for the project. A LG1750 Strut Jib crane was selected to ensure a safe lifting capacity of a 37.5m bridge, weighing approximately 50 tonnes and a maximum lift radius of 80m.
Installation of the bridge commenced on site in early February 2022. The LG1750 Strut Jib crane was erected on site by Global Port Services. The temporary bridge was delivered to site in a number of articulated vehicles. Each 37.5m span consisted of a 24m and 13.5m bridge section that was connected on site ready for lifting.
The site installation team faced a number of challenges with high winds, rain, sleet and snow initially delaying the installation by 4 days. Following discussion and consultation with The Highland Council and Story Contracting, the site team adjusted their working pattern in line with a more favourable weather window to permit the lifting operations to take place . This required a combination of nightshift and dayshift working to ensure the bridge was safely installed. Four 37.5m x 2.5m sections were lifted into place during this period. Janson Bridges site completed the remaining site installation and handover of the bridge on schedule whilst the LG1750 Strut Jib crane was derigged from site by Global Port Services.
Temporary Bridge Installation
Following a site inspection, the temporary bridge was successfully opened to the public on Friday 25th February 2022. This allowed Story Contracting to progress to the next phase of the project with the demolition of the existing bridge and construction of the new bridge.
Temporary Bridge and Diversion Road Opened to Public
A return visit for the Janson Bridges team will be required in October 2022 to remove the temporary bridge once the new bridge has been constructed and opened to the public.