The International Information Center for Geotechnical Engineers

Thursday, 31 May 2018 01:00

Tunnel becomes safe with the usage of Polystyrene blocks

Polystyrene engineering makes old railway tunnel safe Polystyrene engineering makes old railway tunnel safe.

An old and non-operational railway tunnel that lies underneath the approach roads north of the Forth Road Bridge has been made safe by stuffing it with expanded polystyrene blocks.

The 420m tunnel, which runs underneath the roads on the northern approach to the Forth Road Bridge (in Edinburgh, Scotland) is 4.3m wide and 5.1m high, and was degrading. A failure could potentially have had an impact on the roads overhead. The structure originally formed part of the Dunfermline to North Queensferry railway line, providing a link to the ferry service until the opening of the Forth Bridge in 1890 and continuing in limited use for freight until 1954. At first, two options were considered: an ongoing programme of inspection and maintenance or a one-off project to infill the tunnel with a low cost material. The infill option was chosen as more cost-effective in the long term. 

Remarkably, the expanded polystyrene (EPS) blocks have a compressive strength capable of resisting the weight of rock and tunnel lining in the event of a localised failure. However, an additional advantage when compared with concrete or aggregate material solutions is that the EPS blocks can also be easily removed if the tunnel ever needs to be re-opened. The EPS blocks were cut to a size and weight that allowed easy manual handling on site. Another benefit of the lightweight blocks was that they could be delivered in large lorry-loads, reducing the number of vehicle movements required. Once offloaded, the blocks were passed down the access shaft and transported along the tunnel by a sliding monorail system.

The total amount of EPS blocks used was 21,342. The operating company representative for the Forth Bridges Unit Mark Arndt, Amey states: ''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''.

 Sources: BBCGround Engineering

Read 464 times Last modified on Thursday, 31 May 2018 16:26


Disused tunnel at Forth Road Bridge made safe

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