Bransty Tunnel (near Whitehaven): possible solutions?

[Acathater]

Off-the-wall question, but assuming the tunnel floor is undermined by old tunnels and collapsed voids and so useless as a firm surface, how feasible would it be to build something on the lines of a box girder bridge inside the tunnel, supported at the tunnel entrances?

I appreciate the tunnel would need enlarging to take the girder.

 

[ChilliSauce]

Off-the-wall question, but assuming the tunnel floor is undermined by old tunnels and collapsed voids and so useless as a firm surface, how feasible would it be to build something on the lines of a box girder bridge inside the tunnel, supported at the tunnel entrances? I appreciate the tunnel would need enlarging to take the girder

Perhaps the solution might be to pull up all the track and ballast and detect where the voids are under the tunnel .. drill a hole in the tunnel floor at those points and into the void until on firm ground (i.e. the bottom of the old mine working passage) and inject in mass concrete.

== Doublepost prevention - post automatically merged: 16 Feb 2026 ==

Unbelievable to think that when BR went "all out" in the 1980s to try and force closure of the Settle & Carlisle at one point they claimed the Cumbrian Coast line could be used as a Diversionary Route if the WCML was closed / blocked ...

 

[Annetts key]

All these suggestions on how to fix it...

Maybe we should just get MacGyver in to fix it with chewing gum, paperclips and duck tape

 

[HSTEd]

Off-the-wall question, but assuming the tunnel floor is undermined by old tunnels and collapsed voids and so useless as a firm surface, how feasible would it be to build something on the lines of a box girder bridge inside the tunnel, supported at the tunnel entrances?

I appreciate the tunnel would need enlarging to take the girder.

This unfortunately raises the question about the stability of the ground at the ends of the tunnel!

My understanding is that mine workings are all over the place in the area.

Attempting to fill the voids may simply end up with pouring concrete into a bottomless hole until it stops being bottomless. This is a real problem and any of the solutions to fix it could end up very expensive.

The cheapest "solution" is probably just to fill the tunnel bore with foam concrete and give up, but that is politically impractical at the present time.

 

[Bishops]

Perhaps the solution might be to pull up all the track and ballast and detect where the voids are under the tunnel .. drill a hole in the tunnel floor at those points and into the void until on firm ground (i.e. the bottom of the old mine working passage) and inject in mass concrete.

Its ok saying this as a start however you don't know what direction any of the voids go in nor how far down and out they are - you could be pumping for years if it just disappears into the earth and then there is a risk of it getting into the water table

 

[Bletchleyite]

This unfortunately raises the question about the stability of the ground at the ends of the tunnel!

My understanding is that mine workings are all over the place in the area.

Attempting to fill the voids may simply end up with pouring concrete into a bottomless hole until it stops being bottomless. This is a real problem and any of the solutions to fix it could end up very expensive.

It's also a real problem for people with houses etc above the tunnel. If the tunnel could collapse into the mineshaft then so might they. Thus the cost may need spending or mostly spending regardless of the railway - just filling it with concrete isn't necessarily going to provide a viable fix.

 

[HSTEd]

It's also a real problem for people with houses etc above the tunnel. If the tunnel could collapse into the mineshaft then so might they. Thus the cost may need spending or mostly spending regardless of the railway - just filling it with concrete isn't necessarily going to provide a viable fix.

The probability of the houses falling in if the tunnel is filed with foam concrete is likely pretty low.

Most likely the best Net Present Value solution would be to compensate the owners of any houses damaged if and when it happpens.

 

[The exile]

The probability of the houses falling in if the tunnel is filed with foam concrete is likely pretty low.

Most likely the best Net Present Value solution would be to compensate the owners of any houses damaged if and when it happpens.

Filling the railway tunnel with foam concrete won’t help for long if there’s an enormous void underneath it.

 

[HSTEd]

Filling the railway tunnel with foam concrete won’t help for long if there’s an enormous void underneath it.

I think that if the void is large enough to risk the buildings above the tunnel, we are probably getting to the point of asking whether the cost of remedial work exceeds the value of those buildings!

The mine workings could easily run to hundreds of thousands of cubic metres of voidage that would have to be filled to actually solve this problem in the medium to long term.

 

[alf]

I’ve seen many archeology TV programmes where penetrating radar & possibly ultra sound are used to very effectively find unexpected irregularities in underground density.
Could these systems be used to trace voids big enough to be a danger to 10 to 25 tonne axle loads hammering a few feet above the fault?

I hope it is possible; far far cheaper & faster than the destructive testing that comes from drilling & pumping concrete under pressure without knowing how big & widespread the void is.