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Grouted rock anchors in the arctic

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atrizzy

atrizzy

Structural
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Mar 30, 2017
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I'm looking for a survey of peoples' experience with installing rock anchors in arctic conditions.

I'm of the opinion that due to QA/QC reasons alone, this should be avoided. Deep rock anchors will be located in what is essentially frozen bedrock, so good curing of the grout or epoxy in a very deep hole is nearly impossible due to the ambient cold temperatures in the rock, no matter how long you heat the hole for. This seems to me to require pull testing of every anchor. Some even insist on pull testing AFTER a full winter cycle, potentially delaying construction significantly.

HOWEVER... I see that it has been done, often even. So somebody clearly has no issue with it!

Eager to hear from all of you as to what I'm missing, your experiences, and anything else you might want to add.

Thanks in advance!
 
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This is a prime example of where theoretical engineering must take a back seat to practical constructability. Personally I would recommend conventional cementious grout made using hot water. The real trick is to eliminate all air voids within the grout. This can be be achieved by physically raising the anchor within the hole a few times and allowing the buoyancy effect to displace the air.

Knowledge of the virgin rock temperature helps formulate effective practices. Do NOT drill the hole more than about 12 hours prior to anchor installation......the build up of ice within the hole will compromise anchor installation.
 
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Thanks miningman. I'm interested as to how you would QC your recommended solution...
Shouldn't this sort of work include temperature probes during curing? Preheating the rock? Using quick setting (high heat of hydration) grout? Pull tests?
 
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Arizzy, there is a lot I could recommend here, but fundamentally , I would never use temperature probes nor preheating the rock. I would never do pull tests on the anchors that are to be utilised... I might drill a couple of test holes with the proposed geometry and pull test those prior to grouting the real holes. If sub optimal results result , re examine your installation techniques. Dont think I would use hi early set but I would use microfine cement rather than type 10 or 30.

What is your hole diameter?? What is your anchor diameter and length?? How are you going to ensure the anchors are completely clean of oil/ grease?? When is your installation proposed for, ie ambient temperature of minus 30 or plus 10??


Rather than conventional cementious grout , have you considered drill cuttings and water slurry?? depending of site conditions this can be effective.
 
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What about anchor strand material? In the cold conditions, do you have a brittle failure concern? Can you even get charpy tested rebar stock or prestress strand if you want to try and test for it? Can you use the higher strength materials that are often used in rock anchor applications given the lower ductility that normally comes with them?
 
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TLHS, absolutely. These are all concerns, especially since the anchors are being used for providing fixed connections for a massive plant building. If there's no monitoring possible and something happens, the building will potentially become unstable.

With strand type rock anchors, I'd be worried about corrosion potential as well.
 
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atrizzy, strand and threaded bar ground anchors (tieback and tiedown anchors) are routinely used for permanent applications where corrosion is a consideration. Review ground anchor corrosion (edited) information in catalogs from Williams Form Engineering, Nucor Skyline Steel, Dywidag, and other suppliers. They have a ton of information, but nothing on arctic conditions. That's why I referred you to PTI (The Post-Tensioning Institute).

 
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Gentlemen , recent posts altho undoubtedly well intentioned, are missing the critical issues here. Its not the low ambient temperature thats the issue, its the fact that the installation is in permafrost. I doubt that any USA standards are really relevant. There may be some Corps of Engineers documentation that relates to Alaska and pipelines , but the geology of those areas are totally different to the Canadian precambrian shield that exists across the NWT.

I have installed rock anchors as long as 20 metres. If the OP really wants to research large industrial plants in permafrost conditions, search for details of problems experienced at Nanisivik minesite on Baffin Island
 
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