Degrading tunnel in Fife filled with polystyrene
A disused railway tunnel underneath the approach roads north of the Forth Road Bridge has been filled in after it was found to be degrading.
It was part of the Dunfermline to North Queensferry railway line, providing a link to the ferry until the opening of the Forth Bridge in 1890. It continued to be used for freight until 1954.
The tunnel runs underneath the A9000 and B981.
It is 420m (459 yards) long, 4.3m (14ft) wide and 5.1m (17ft) high.
It has a vaulted roof and brick lining. Both ends 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.
Amey engineers carried out a structural inspection in February 2016, finding that parts of the tunnel were degrading and in need of preventative maintenance.
Two options were considered: an ongoing programme of inspection and maintenance, or a one-off project to fill the tunnel with a low-cost material.
The filling option was chosen as it would stop the need for future inspections or maintenance.
The tunnel has been filled with expanded polystyrene (EPS) blocks, which can be easily removed if the tunnel ever needs to be reopened.
The blocks were passed down the access shaft and transported along the tunnel to the work face hooked onto a specially designed sliding monorail system.
The tunnel was lined with a hydrocarbon resistant membrane, before a total of 21,342 blocks were installed.
Once the body of the tunnel was filled, the access shafts were filled with concrete to seal the tunnel.
Mark Arndt, Amey's operating company representative for the Forth Bridges Unit, said: "This has been an unusual and interesting project where we've 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."