Polystyrene engineering makes old railway tunnel safe

[Adlington]

A disused railway tunnel underneath the approach roads to the Forth Road Bridge has been made safe with giant polystyrene blocks.

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.

Amey engineers carried out a structural inspection in February 2016, finding that parts of the tunnel were degrading and in need of preventative maintenance.

The unusual feat of engineering uses lightweight expanded polystyrene (EPS) which can be easily removed if the tunnel ever needs to be reopened.

Source (BBC)

Tried to find out more about EPS, also known as Styrofoam(TM), so asked uncle Google, and got loads of information along these lines: lightweight, good thermal insulation, inert in nature, durable, shock absorbing properties, perfect for packaging cooked food and perishable items, can be used as insulated panels , as flotation material in the construction of marinas and pontoons and as a lightweight fill in road and railway construction.

Nowhere does it mention strength and load bearing properties... So why is it used for making a crumbling tunnel safe??

 

[Dr_Intoxicated]

It has been used in constructing road embankments for several years. I heard an engineer describe its use whilst listening to desert island discs!

http://www.geofoam.org/applications/road-construction/

 

[pdeaves]

It has been used in constructing road embankments for several years

And some railway platforms and, I believe, railway embankments.

 

[yorksrob]

I read about this on the BBC. It's a good idea because it preserves the tunnel for future use.

(Shame this solution wasn't available for Thackley old tunnel !).

 

[swt_passenger]

I read about this on the BBC. It's a good idea because it preserves the tunnel for future use.
.

Pretty much academic in the case of that tunnel, I’d have thought, unless there’s a cunning plan to remove the bridge approaches. AIUI both portals were already completely buried and the workers entered through existing shafts, now capped.

 

[swt_passenger]

Cow Lane bridge under Reading West curve is an example of using lightweight blocks to rebuild the embankment. I expect use is relatively widespread nowadays but unless someone sees it being done at the time the evidence is by its nature quickly hidden.
Around 3 mins in:

 

[swt_passenger]

Nowhere does it mention strength and load bearing properties... So why is it used for making a crumbling tunnel safe??

It’s fundamentally safe because the load is spread evenly over a very wide area. It wouldn’t be strong at all if the same load appeared acting at a single point.

 

[yorksrob]

Pretty much academic in the case of that tunnel, I’d have thought, unless there’s a cunning plan to remove the bridge approaches. AIUI both portals were already completely buried and the workers entered through existing shafts, now capped.

It wouldn't necessarily be reused for a railway. Although in the example of Thackley old tunnel, an extra couple of tracks between Leeds and Shipley would be handy.

 

[Ploughman]

The embankment at Irlam was done with these a number of years back I think.

 

[Hellzapoppin]

The platform widening at Bath Spa station used EPS units. Really quick to install, level the ground, bed of sand or screed, install the units and lower the copers on top. In Bath the units were faced with tiles which clipped into rails set into the EPS.

 

[Ploughman]

It wouldn't necessarily be reused for a railway. Although in the example of Thackley old tunnel, an extra couple of tracks between Leeds and Shipley would be handy.

The only bug bear down that stretch would be trying to squeeze another pair of tracks in past Farnell's between Kirkstall loops and Armley Jn.

 

[Pete_uk]

The thing with polystyrene, like most substances, is very strong when used in the right way. If this stuff is used the right way I have no doubt it will keep the bricks up.

 

[mde]

And some railway platforms and, I believe, railway embankments.

If I remember correctly it was used in Glasgow Queen St platform extensions during the tunnel works (with a surface overlaid on top so the concourse remains usable in the interim). It's certainly an interesting material for this context.

 

[GRALISTAIR]

If I can find my photos I will post. I rebuilt a floor in Lytham St Annes in 2004.
1. Dug it out to about 18 inches deep
2. Visqueen sheet
3. Stoned it up with 2 inch crusher Run
4.Huge polystyrene foam blocks
5. Rebar cage
6. 9 inches of concrete
7. Troweled up to a polished finish
8. Tiled up

Great floor and very warm those PS blocks are great and warm and insulating

 

[jopsuk]

Further: it isn't about supporting the wight of the ground above. If the bricks are held in place, then even cracked and broken they'll still transmit the weight through the arch, mainly. So most of the weight the EPS has to hold up is just the actual bricks.

 

[Adlington]

It’s fundamentally safe because the load is spread evenly over a very wide area. It wouldn’t be strong at all if the same load appeared acting at a single point.

Makes sense. Thanks for the explanation.

 

[Skie]

Much of Liverpool 1's undeground carpark has this on the roof to support and build up the park on top without adding too much extra wait on the structure below. It's a fairly common technique.

 

[broadgage]

EPS is not particularly strong, but can support astonishing weights in total if these are spread over a large area.

IIRC part of the line into London Victoria is supported on EPS used to replace a suspect viaduct.
More recently during the rebuilding of Reading station, during overnight possessions, EPS blocks were used to infill the space between platforms, over the rails and up to platform height. After protecting the tops of the blocks with either plywood or lightweight steel plates, heavy plant and machines were driven from one platform to the other. The large EPS blocks were carried by two men IIRC.

The main hazard of using EPS is flooding, if the groundwater rises up around the blocks then they will "try" to float with an upwards force of many tons. This can displace and damage whatever is above. Hopefully this has been allowed for ! deep inside a tunnel the uplift may not matter since the weight of soil above should exceed the uplift force. Any part of the tunnel at a shallow depth might be at risk.

 

[John Webb]

I recall reading about the use of these blocks in "New Civil Engineer" in the late 1980s-early 1990s, so the technique has been around for quite some time.

 

[hwl]

Also seen under the tracks and platforms at London Bridge during the rebuild under P6-9 at the Western end above the original William IV part of the station (adjacent to the new wing of the upper concourse currently under construction). The new bigger (wider) structure weight had to match the old while taking higher loads. A second viaduct was build above the original one to create the high level station in 1866 when the railway was extended to Cannon Street and later Charing Cross and the EPS was used as part of a new structure to replace the 1860s one with new wider alignment.

EPS also eliminates voids that need periodic inspection in the future

 

[thebigcheese]

Are they fairly rodent proof? Seems ideal for rats to burrow into.

 

[talltim]

Sheffield platform 5 also has EPS unside some of it.

 

[randyrippley]

Start by reading these two
http://www.sundolitt.co.uk/sundolitt-uk-home/construction/eps-civil-engineering-benefits
http://www.epsindustry.org/building-construction/compressive-strength

between them you'll get a good idea of the strength of EPS

 

[bspahh]

I recall reading about the use of these blocks in "New Civil Engineer" in the late 1980s-early 1990s, so the technique has been around for quite some time.

This bridge across Abbey Barn Lane on the M40 https://goo.gl/maps/nXGdQwLpdwx was built in the early 1970s. I remember that you could climb up under this, and see a layer of expanded polystyrene in the bridge.

 

[transmanche]

Recently, in Newcastle upon Tyne, the Cowgate roundabout (and pedestrian subways) was infilled with polystyrene blocks and the new road constructed on top.

See this report from the Evening Chronicle, or this video from the City Council: