Resin bolt repair

[Badlad]

Moderator comment: new thread created form posts in "Resin bolt removal" as requested by participant. See https://ukcaving.com/board/index.php?threads/resin-bolt-removal.34572/

I wonder if there could be a different solution to removing loose resin anchors.
I understand the forces required to remove the anchor are still very high even though there is some rotation in the hole. The only problem for these anchors seems to be a loss of the resin/stone bond due to shrinkage.
Is it possible to inject a resin into the gap to solidify the anchor again in situ.?
I had a job once on the stone urns of the Radcliffe Camera building at Oxford University. The stone urns had cracked and we had to inject them with a deep penetrative resin to rebond them together. Most of the crack surface was sealed and a small diameter hole drilled into the crack to inject the resin. I wonder if something like this was worth working on considering the amount of loosening anchors that are predicted across the caving areas and all the difficulties removing and replacing them entails.

 

[ChrisB]

Is it possible to inject a resin into the gap to solidify the anchor again in situ

I don't see why not, I've done similar things on cracked concrete. I think it would need a different and less viscous resin, which might mean that the anchor no longer met the manufacturer's recommendations. That ought not to be a problem for recreational cavers but might be concern for instructors. Do we know whether the crack is typically between anchor and resin or resin and hole?

I hope to be at Pete's workshop and we can talk about it there.

 

[andrewmcleod]

The bond between the rock and the resin is really quite important for a resin-bonded anchor... given the difficulty of getting a good resin-rock bond in the first place (requiring careful hole preparation and cleaning), I can't imagine any re-injection is going to give you a reliably-strong result? (at least it sounds like a considerable testing project for someone which is probably a lot more faff than just pulling the anchor out anyway with a suitable puller)
When anchors are being reinstalled in the same hole, I think it's standard practice to drill out all the remaining resin before starting (presumably because resin-resin bonding would introduce another uncertainty to the process).

I think it would need a different and less viscous resin, which might mean that the anchor no longer met the manufacturer's recommendations.

As an aside, I'm not sure 'manufacturer's recommendations' hold quite as much meaning for the IC anchor which after all is not a commercial anchor and has not been CE standard-ed...

 

[mikem]

If you can't easily pull the bolt out when it's a little bit loose, then adding more resin could potentially stop it turning - certainly not going to weaken it - whilst doing pull tests potentially does

 

[pwhole]

Does anyone know for certain whether the resins generally expand very slightly on curing? If the adhesion is only from friction alone, the bond is remarkably strong, considering how difficult it is to rough up the hole before injection. Unless the hole is 'rough enough' at the microscopic level already? I do admit to not being entirely certain on this.

 

[mikem]

Most bolts don't load along their main axis, so are actually levering across the hole & creating friction that way (but also means they are affecting the resin, as it presumably doesn't cure further back in the hole as quickly as the surface - not sure how many are air activated?)

 

[IanWalker]

The idea of leaving the defective anchors in-situ is appealling, but needs careful consideration. I've mulled over some of the advantages and disadvantages before and after talking with others have decided to drop it for the time being.

The main issues seem to be (1) how loose is 'loose', and is in-out movement included or just round-and-round movement, (2) unknown strength of a loose anchor and (3) difficlty of repeatability in repair.

I understand the forces required to remove the anchor are still very high even though there is some rotation in the hole. The only problem for these anchors seems to be a loss of the resin/stone bond due to shrinkage.

Best we can say is removal of loose anchors requires a variable amount of force. Some come out easily and others not-so.

We could say they 'typically' or 'often' are difficult to remove but this is by no means true for all cases.

Looking at removed anchors it is clear that many pull out without deforming the eye - an indication that they haven't reached the 10kN to 19kN range previously reported for deforming a DMM eye.

So we cannot say that loose anchors require 'high forces' to remove. We can't quantify how much force it takes to remove a loose anchor or what the range is or the influencing variables. We cannot say they are 'safe' and just need locking in place.

We could test some, however this would be destructive to the caves and still only present us with data for those we test. By nature of the variability of loose anchors we would need to test a very large number to be sure of statistical confidence. Such a test would take a long time and pull resources from anchor replacement as it would likely be the same people doing the work.

For comparison, previous testing of new anchors in new clean holes with ideal placement conditions (downward in a quarry) required 32 pull tests to destruction, in order to be statistically confident of the sample result applying to the popultation as a whole. That's to prove that a programme of new and well-installed anchors are safe enough.

Is it possible to inject a resin into the gap to solidify the anchor again in situ.?

I don't know about this. The main issue to resolve would be how to ensure the gap is filled, given that you can't see inside. Someone suggested that you could drill out 'some' resin and then add fresh resin to stop the rotation. But any process would need to be repeatable in cave conditions and not damage the anchor legs.

The resin you put in would not prevent continued shinkage of the old resin, meaning a loose anchor might be injected in 2026, but become loose again in a few years time. (We don't know nearly enough about the rate of shrinkage to be able to quantify this. Also the resin you inject would have some shinkage of its own.

At best, you would end up with an old anchor and old resin that stays in use a bit longer (life extension). We'll still need a proceedure for replacement in the long term, and another visit.

In the meantime, we have an already large number of anchor types and resins historically used. Some now denounced and rejected, but at least identifiable to those in the know. To overlay repairs we'd need a level of training and rigour of record keeping above and beyond what we have demonstrated historically.

Does any manufacturer currently give guidance or products for repair of a loose old anchor that has unknown resin? If it was possible to do it seems likely someone would commercialise it

The whole lot seems to be a sticking plaster and avoiding the main issue that we have loose anchors when they are not meant to be loose. That being said, I'm pleased the issue is being acknowledged and receiving attention.

 

[IanWalker]

The bond between the rock and the resin is really quite important for a resin-bonded anchor... given the difficulty of getting a good resin-rock bond in the first place (requiring careful hole preparation and cleaning), I can't imagine any re-injection is going to give you a reliably-strong result?

Yes, the injected gap would need to be clean (how) and emptied of water (how) in order to allow the resin in.

 

[IanWalker]

Does anyone know for certain whether the resins generally expand very slightly on curing? If the adhesion is only from friction alone, the bond is remarkably strong

I am not a resin expert, but my understanding is that currently used resins all shrink on setting, and possibly on an ongoing basis.

They are remarkably strong unless they are loose in which case there is no bond at all.

 

[mikem]

If the gap wasn't filled then they would continue to move. But even if they are loose, they are generally very hard to pull out

 

[paul]

Moderator comment: Posts regarding Bolt resin recommendations moved to new thread at previous poster's request to keep this one on topic about bolt repair. See https://ukcaving.com/board/index.php?threads/bolt-resin-recommendations.34589/