Tunnel Re-boring

[matacaster]

No, in fact non-circular sections are generally easier in hard rock than in soft material, the difference being that hard rock is essentially self-supporting and the tunnel lining is there to stop loose bits of rock falling off, whereas the tunnel lining in soft material has to support the weight of the ground above it and a circular arch is more structurally efficient.

Of course if you're using a TBM it will be circular no matter what your ground conditions, unless you have one of these:
View attachment 99420

I believe that older tunnels through soft material often had several courses of brick to support the ground above. In such tunnels, is it possible to remove such linings and replace with a thinner but stronger concrete lining thus improving gauge clearance?

 

[edwin_m]

I believe that older tunnels through soft material often had several courses of brick to support the ground above. In such tunnels, is it possible to remove such linings and replace with a thinner but stronger concrete lining thus improving gauge clearance?

If you do that there would be a huge risk of the whole thing collapsing.

 

[GRALISTAIR]

If you do that there would be a huge risk of the whole thing collapsing.

Exactly

 

[matacaster]

If you do that there would be a huge risk of the whole thing collapsing.

I suppose that might be a little inconvenient then! I thought I'd read somewhere that some but not all of several layers of brick linings had been removed - can't remember where though and i might have not remembered correctly.

 

[gingertom]

I suppose that might be a little inconvenient then! I thought I'd read somewhere that some but not all of several layers of brick linings had been removed - can't remember where though and i might have not remembered correctly.

wondering then how they managed to build it in the first place without it collapsing.

 

[edwin_m]

wondering then how they managed to build it in the first place without it collapsing.

Mortaring each brick into place is a bit different from trying to break it apart and finding huge pieces may fall out back to wherever the mortar is a bit weaker. Not saying it can't be done, but I doubt it could be done quickly.

 

[gingertom]

Mortaring each brick into place is a bit different from trying to break it apart and finding huge pieces may fall out back to wherever the mortar is a bit weaker. Not saying it can't be done, but I doubt it could be done quickly.

I agree with you there. whilst it could be done it would be a long drawn out tedious process, making it very expensive. Makes it unlikely, unless the costs stack up or there is no alternative but to bite the bullet.

 

[snowball]

The August issue of Modern Railways has a short piece on the Trans-Pennine upgrade on page 9, including this:

Previous suggestions by Network Rail that some of the tunnels on the route would prove too difficult to electrify are now being rolled back; only around 1% of Standedge Tunnel would need additional work for wiring and clearance for W12 gauge freight trains. Scout Tunnel, at 188m long, is more challenging but is shorter than the 270m Farnworth Tunnel which was re-bored in 2015.

Stalybridge Tunnel isn't mentioned.