M8 Woodside viaducts project
The M8 Woodside Viaducts are a vital element of the strategic motorway and road network serving Glasgow, the wider region and country. They are estimated to carry approximately 150,000 vehicles per day.
Ahead of planned refurbishment work, intrusive inspections of the supports were completed in 2020 and 2021 to help determine the extent of repairs. These found that the viaducts’ crossheads were in a much worse condition than anticipated which then required the implementation of temporary traffic management, lane closures and slip road restrictions in March 2021 to reduce the traffic load on the viaducts. Temporary propping works are currently being undertaken which, when complete, will allow the traffic restrictions to be lifted and allow more extensive repairs to be undertaken to the crossheads.
We acknowledge the disruption that is being experienced by the travelling public as a result of the ongoing temporary propping works and appreciate the patience of road users. However, we continue to work closely with the Contractor to ensure that the works are delivered safely and at the earliest opportunity.
What is involved?
Amey PLC is carrying out the works on the M8 Woodside Viaducts on behalf of Transport Scotland. This is a complex and challenging project with propping works currently underway to remove load from the affected supports. Once the viaducts have been propped, repairs to the deteriorated support element (known as the half-joint), will be carried out.
A total of 23 supports are required to be propped. Each support requires individual propping designs to take account of the varying column heights, span length and widths resulting in different loads to be supported by the props. The propping foundations at some locations are affected by a number of buried services (such as gas and water mains) as well as Strathclyde Passenger Travel’s (SPT) subway tunnels. These services have a major impact on the propping solutions available.
To remove the load from the half-joints the viaducts will be jacked. This process involves transferring the loading from the existing supports and into the temporary propping system. Once jacking has taken place, repairs to the half-joints will be carried out and finally the jacks and temporary propping will be removed.
At four locations around the SPT subway tunnels, special structures will be constructed to allow these areas to be propped and the load to be transferred to areas which don’t affect the tunnels. Another location will be propped using a steel collar around the existing columns to mitigate any load being exerted on underground services. Again, once repairs are completed at these locations, the jacks and propping can be removed.
The first stage of the construction programme involving excavations, piling and other groundworks around the existing viaduct columns commenced in August 2021. The installation of the props at the first of the 23 locations followed in February 2022.
When will it be completed?
Completion of the propping and jacking work - which will result in the removal of lane restrictions on the M8 - is expected to be completed in early 2026. However, the Contractor, Amey PLC is working towards delivering the eastbound carriageway sooner, in Summer 2025. They are also exploring opportunities to bring work forward where possible. These dates are subject to change due to unforeseen circumstances such as adverse weather or unexpected service diversions.
How much will it cost?
The cost of undertaking the temporary propping is estimated to be between £126m - £152m, including baseline cost, risk, inflation and a contingency allowance. The repair costs are currently in development.
How will it affect me and what is being done to reduce disruption?
To ensure the safety of road workers and the travelling public, speed and lane restrictions are in place on the M8 for the full length of both viaducts; the eastbound on-slip road at Junction 17, and westbound on-slip at Junction 15 and nearside off-slip at Junction 17 are closed. Slip roads at Junctions 16 and 18 remain open. Signed diversion routes are in operation.
Narrowed lanes have been introduced on the main carriageway of the M8 over the viaducts. HGVs are being encouraged to consider using an alternative route via the M74 where possible due to these narrow sections.
The local road network is also affected and signed diversions are in operation.
The Temporary Propping works aim to minimise disruption as far as possible whilst keeping this stretch of the motorway open to the 150,000 vehicles that use it on a daily basis.
The traffic management will be removed once all the required propping works have been completed.