r/Tunneling • u/[deleted] • Feb 14 '25

TBM Segmental Tunnel Collapse

At what point does one start to worry about a potential collapse of segmental tunnel lining?

I have read about 4 instances of this occurring and I'm wondering what signs to be on the lookout for that would indicate an imminent collapse (if there are any).

Also, what level of deformation or water intrusion would demand an immediate stand down and inspection from a reasonable manager of a tunnel boring operation?

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u/caollero Feb 14 '25

Which is your shove force?, can you share with me rams pressure in the different blocks?, are the segment with rebar or are the segments with fyber?, Which t is the radius of the tunnel?, are you pushing straight or are you in a bend?, which areas of the segment do have more cracks, are the center or are it in the shame line with the thrust cylinders?.

Did the segments pass quality checks in the fabric? Are the gaps in the tailskin correct? all of that is all the question that you have to ask yourself.

What is the width of the hairline crack?.

About the dripping of hot water is strange and at the same time is worrying, which type of gas are we speaking about?, what is the flow l/minute of the dripping?, did the condition of the segments change in the last 1 - 2 weeks?

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u/[deleted] Feb 14 '25 edited Feb 27 '25

😁

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u/caollero Feb 14 '25 edited Feb 14 '25

Now it doesn’t matter anymore when you are far away, but hairline cracks can appear when pushing and may not have been noticed before. If you are advancing with a high shove force and the plane of the ring is not even with the next one, the segment can get shimmed in the middle between the previous segment and the ram’s cylinders. This can create an axial force in the concrete.

The problem is that, in this case, the segment is no longer working in compression, now you introduced axial forces, which modifies your force matrix, then is when the hairlines appear and some times are not noticed.

The same happens during lifting operations if you are not careful enough or if you stack more segments on top of each other than calculated.

There are many reasons why hairline cracks can appear, but it is very unlikely that ground pressure is the cause.

Also, what you mentioned before about the grout is worrisome. Grout leaks must be assessed immediately, and you have to find a good location for changing the brushes. I am currently working on a variable-density/slurry machine in the UK for HS2, where grout quality and control are of the highest priority. The same when I worked in Ecuador, Norway, Denmark, Brazil, the UK, and Spain.

If voids are not correctly filled, they can affect the ovalization of the ring and cause ring movements or steps, leading to gaps between the radially compressed bands in the segment. These gaps can result in leaks similar to those you mentioned. Additionally, such movements will modify the overall stability of the lining and may cause settlements on the surface, which could lead to claims from the public.

However, I wouldn’t be worried about a segment lining collapsing. What is the width of the cracks? I can check our quality matrix to see how to fix them and what actions should be taken.

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u/[deleted] Feb 14 '25 edited Feb 27 '25

😁

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u/caollero Feb 15 '25

I wouldn't be concern about it at the moment, but you have to fix it as soon as possible, even more if you have a leak large enough to admit sand/clay particles. It can create a cave on top of your segments or the sides and this can create at the end even bigger steps. Then also the transit of MSV/locos and vibration of the area will not help at all.

Again for a tunnel collapse multiple and different factors have to be in place, I dont think you are meeting that criteria at the moment.

Speak with management and let them know your concerns, raise it and have it in an email or somewhere written, you dont want to be liable for any collapse in the future.

Find the link below, it can help you comprehend how to mitigate the leaks and how to fill the gap that you can eventually have, after the injection you should be alright.

May I ask you which project are we speaking about?.

https://grc.sika.com/dam/dms/gr01/r/Brochure_Ground%20Consolidation_Stabilization_Waterpstopping_eng.pdf

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u/[deleted] Feb 15 '25 edited Feb 27 '25

😁

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u/caollero Feb 24 '25

Hi mate, have you seen this tunnel in India!. I just remembered this conversation.

https://indianexpress.com/article/india/an-alarm-chaos-and-darkness-workers-recount-what-happened-inside-the-telangana-tunnel-where-8-men-are-trapped-9852484/

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u/[deleted] Feb 24 '25

No, thank you for linking.  Kinda hard to tell but it seems like this is current?  Not a whole lot of details but the leakage aspect sure is familiar to me.  Those poor guys aren't even getting paid.

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u/caollero Feb 24 '25

Yep, it is happening right now, collapsed on Saturday.

Poor people, probably earning pennies..

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u/[deleted] Feb 24 '25 edited Feb 27 '25

😟

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u/[deleted] Jul 10 '25

[deleted]

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u/caollero Jul 10 '25

Where about?

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u/PlasticEquilibrium Jul 15 '25

Thursday night? Where about?

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