Post-drilling for electrical fixtures and utilities effect on tunnel lining segments

[Kareem Eltouny]

Greetings,

I've a question regarding the post-drilling and post-installation of anchorage / fixtures for utilities in TBM tunnels.
Does post-drilling for installing anchors in tunnel lining segments affects durability of the precast segments? as they reduce the concrete cover while drilling they may lessen the protection against corrosion and fire for steel reinforcement.
I've been searching the web for a week now with no results regarding this matter.

Thanks in advance.

 

[oldestguy]

Why not ask directly of those that maintain the tunnels. You might find information as to who might help yu via that question from the associations.

http://tunnelingonline.com/

 

[MotorCity]

The anchors should not be installed directly over locations of reinforcement. You run the risk of drilling through the reinforcing and/or reducing the cover as you suggest. Find where the reinforcement is located and drill elsewhere.

 

[Kareem Eltouny]

Thanks oldestguy for the website, and thanks MotorCity for the response, does that mean that anchors should be installed after using an instrument to know reinforcement locations first? this will take too much effort for installing fixture in a 5 kilometers tunnel, maybe there is a faster way to do this?

 

[MotorCity]

You have a couple of options. Field locate the bars using X-ray, GPR or similar, pull out the shop drawings for the panels and you may be able to measure where the bars are located, or install inserts into the precast for attaching items later in the field (sounds like this is not an option for you). If you want to see what can go wrong with anchors in tunnel projects, just google "Big Dig". Obviously its not the same as your situation but a good reminder nonetheless.

 

[Kareem Eltouny]

Thanks MotorCity for your help,
I've been searching lately (for almost two weeks) for any reference that describes how drilling in concrete affects durability of the tunnel lining without any luck. If you've got any reference (book, paper, article anything) please let me know.