A disused railway tunnel near the Forth Road Bridge has been filled in – without anyone knowing work was being done!
It originally formed part of the Dunfermline to North Queensferry railway line which provided a link to the ferry service until the opening of the Forth Bridge in 1890.
It continued in limited use for freight until 1954.
The tunnel ran under the A9000 and B981 on the northern approach to the Forth Road Bridge, and engineers from Amey, the bridges’ operating company, were called in after it was found to be disintegrating.
Both ends of the 420 metres tunnel had been sealed off, and the adjacent cuttings filled in, so the only remaining means of access was via a vertical shaft at each end.
Engineers carried out a structural inspection in February 2016, and found parts were degrading and in need of preventative maintenance to ensure continuing structural integrity.
Due to the limited depth of cover above the tunnel, a failure could potentially have had an impact on the roads overhead.
Two options were considered – an ongoing programme of inspection and maintenance, or a one-off project to fill it in with a low cost material.
It was decided to fill the tunnel with expanded polystyrene (EPS) blocks manufactured to a specific compressive strength capable of resisting the weight of rock and tunnel lining in the event of a localised failure. Unlike with concrete or aggregate material, they can also be easily removed if the tunnel ever needs to be reopened.
As part of the work, local primary school children from Burntisland and Lauriston were invited to fill two time capsules with items of their choice. These were then buried in the tunnel amongst the blocks.
Mark Arndt, Amey’s operating company representative for the Forth Bridges Unit, said: “This was an unusual and interesting project where we learned something new about the history of the area as well as gaining the satisfaction of making a disused tunnel safe.
“The team deserves particular credit for developing innovative solutions that maximised workforce safety while minimising the cost to the public purse and the impact on local communities.
“It’s a real measure of success that most local residents were not even aware this work was taking place, despite the tunnel emerging within metres of homes in North Queensferry.”