Loose resin anchors

Recently it was reported to me that there were two loose anchors in Heron Pot. Me and Graham Coates pulled them out and replaced them with IC anchors. Here is a photo of one of them.



The ones in Heron both rotated by about 3mm and the resin to rock bond had gone. When they were pulled out most of the resin came out with them. They are DMM anchors and will have been installed in the early 1990s probably using Hilti resin. I have been told that there are also some loose anchors in Swinsto and today I was told that there is a loose anchor at the top of Gaping Gill. We need to find out how many more loose anchors there are and where they are so that they can all be replaced.

We need to be able to identify if there is a risk associated with anchors of a particular age, installed using a particular type or batch of resin or exposed to particular environmental conditions and to do that we need information.

Please report all loose resin anchors that you know about in the northern region even if you have reported them in the past. Please report them on here, to me via the email address on the IC website or via the CNCC reporting email (which now goes to the CNCC Secretary).

Certainly looks like a resin failure or an installing error, the anchor looks fine.
I hope the records identify the resin batch, was this BCA resin, used in other areas?

EDIT- (Or was it NCA back then? - brain gone, scm!! )

Good work.

What force was needed to extract them?


CNCC Anchor reporting form

ianball11 said:

[emoji106]

What force was needed to extract them?


CNCC Anchor reporting form

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Given the deformation of the bar... Lots I imagine.. Probably forces well in excess of those that your SRT kit or rope could withstand.

Not that I'm saying that it shouldn't have been replaced, just trying to bring a little perspective and suggesting that nobody loses any sleep over the odd resin bolt being a bit loose.

Indeed. Unless they rig everything off a single one. No-one would ever be stooooopids enough to do that, though.

In my latest report to the CNCC I have said that the installers group will give the highest priority to replacing anchors which are deemed to be dangerous. That includes any wobbly resin anchors.

The anchor in the photo was in a position where there could be a direct outwards pull on it as someone leaned out to clip the anchors at the head of the pitch. If it failed the caver could have taken a pendulum fall of about 3m and hit the wall before being trapped by the force of water directly under the waterfall.

You can make wild guesses about how much force might be required to extract a wobbly anchor if you want to but I don't think the BCA's insurers would take much notice.

I just remembered Diccan. We know about that loose anchor. It maybe should have been done during the very dry weather that we have had this summer but now it's the start of the wet.

Simon Wilson said:

We need to be able to identify if there is a risk associated with anchors of a particular age, installed using a particular type or batch of resin or exposed to particular environmental conditions and to do that we need information.

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That's sensible

ianball11 said:

What force was needed to extract them?


CNCC Anchor reporting form

Click to expand...

That's a sensible question

Simon Wilson said:

You can make wild guesses about how much force might be required to extract a wobbly anchor if you want to but I don't think the BCA's insurers would take much notice.

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That's not a sensible answer.

Simon, thanks for suggesting we report any on here.

Of that line of anchors around the right wall at the top of GG Main Shaft the final one is slightly loose. (This line of anchors is made use of for safety by those who build the gantry for GG winch meets, so they do get used at least 4 times a year, tackling and de-tackling, as well as general caving use.)

Happen worth your having a glance next time you're up that way?

Glad I asked.

There's a removal tool that does not measure the force and which has been used in several caves including Heron and there is a test puller which is much bigger.

http://www.resinanchor.co.uk/5.html

The loose anchor at GG might be easier to get the test puller to so I can measure how much force it takes.

However, I think it pretty much irrelevant how much force it takes. If an anchor has been reported as being defective I am assuming it will not be covered by the BCA insurance and we would not be acting responsibly if we didn't remove it.

With the loose anchors I have seen, the resin seems to have shrunk and broken free of the rock all around. They were only held in place by irregularities in the hole. If one loose anchor took, say, 10kN to extract it is still anybody's guess how much the next loose anchor would take. Is anybody seriously suggesting any of them should not be removed?

Good post, as for your question I can only answer that for myself, no.

Well said Simon; an excellent response.

ianball11 said:

What force was needed to extract them?

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For what it is worth, see last page of http://www.cncc.org.uk/doc/3.  I have observed some 'loose' anchors jam in the rock when subject to a partial extraction force.  I presume this jamming is due to 'mechanical' interference between the resin and the rock since the chemical bond has gone between the rock and the resin.  But if they work loose again, then presumably either the rock or the resin is wearing away.  So the anchor might well 'pop out' at some stage.

I apologise. I might have been assuming people understand more about the bonding of anchors than they actually do.

The minimum extraction force required by the relevant UIAA standard is 20kN (20 kilonewtons or about 2 tonnes force) and that is ideally what we would want all in-situ anchors to be able to withstand.

A minimum of 20kN is what the IC anchor is designed and tested to withstand.

If the resin plug was detached from the rock and wobbling about in the hole, I think it is safe to assume that the extraction force would be significantly reduced.

The bonding of a resin / glue in anchor and its behavior on being pulled out is surprisingly complex.  So I will make a plug for my lecture on "Recent Developments with Anchors" at the forthcoming Hidden Earth where I will touch on the topic.

I don't know if the loose P bolt at the top of the big pitch in Hardrawkin ever got fixed - I haven't been back there recently.

Thanks Rachel. Does anybody have any more information about this loose anchor?

All of the loose anchors that I know about are in caves that were equipped in the early 90s when the resin used was Hilti resin. A guesstimate is that there might be something around a thousand anchors fixed with Hilti resin. Those anchors were paid for by the BCA (NCA) and so if you are a BCA member they are your anchors. There is no system of routine inspection in the BCA anchor policy; instead it makes you the inspector of your anchors.

BCA Anchor Policy item 7.
http://british-caving.org.uk/wiki3/lib/exe/fetch.php?media=equipment_techniques:anchor_policy_2013.pdf

Please closely inspect all anchors. Do not overlook even the slightest movement. If there is any discernible movement then it is a loose anchor and needs to be reported. We need to know about loose anchors because we need to find out the scale of the problem and if it is a growing problem.

Hi Simon, it might be worth a chat with DCA's equipment officer as we've had a fair few wobbly anchors reported in the last couple of years. Off the top of my head we've replaced or are needing to replace 2 anchors in P8, 1 in Giants, 1 in Suicide, 1 in Rowter and possibly more. These are P bolts and I suspect are from the same installation period as yours so similar techniques and resin I bet. I raised the question myself about this indicating a possible issue with anchors or this age or specification.
Pete Knight
DCA Projects