To bolt or not to bolt?

[Jopo]

Whilst we are all ruminating on a 'better' (?) test would it not be in order to include a way of testing for a shear load, preferably dynamic, to represent what a anchor may be subjected to, rather than a simple ( but easy to achieve ) tensile pull test.

The present test proves that the anchor is capable of very high loads, taken that it is correctly installed, when subjected to a progressive pull in the direction it is not generally expected to be used.
Is it not more pertinant to test the anchor in the mode it is most often used - and to satisfy the worst case a, fall factor 2 with the BS standard load of 100k. To remove some of the variables, (knots and different ropes), a drop test would be better using a steel chain.

Or am I missing something.
Incidentally, are other types of anchors being considered to replace resin bonded P hangers?

Jopo

 

[cap n chris]

I recall seeing a photo of a deformed anchor which had been sheer loaded to destruction; IIRC it had required a massive, unachievable*, load to result in the deformation.

* In a cave rigging scenario.

 

[ChrisB]

Test loading direction and strength of concrete are both significant in devising a test regime. There are two questions to be answered by testing:

1. is this design of anchor - resin - hole - rock suitable?

2. is a particular anchor correctly installed in suitable rock?

The test for each of these can be different. Testing the design should establish what the failure mode is, under various credible cave loading scenarios. For different designs, it might be resin failure, it might be bending of the anchor, it might be crushing of the rock or cone pullout. For rock strength, what matters is the rock strength above which something else is the critical failure mode. In other words,  provided the rock is at least X strong, there's no point in it being stronger. So If you are in that range, you don't need to know the rock strength very accurately.

Testing installation is concerned with resin placement and rock strength / planes of weakness. A pull out tests these quite well. No need to test shear load, as it won't be critical.

Most cave use is, I think, predominantly shear load, but something like a Y hang from opposite walls could be 45º, and that's quite a pullout. How many people learn rigging with consideration of the loading on the anchors?

Chris

 

[spikey]

Most cave use is, I think, predominantly shear load, but something like a Y hang from opposite walls could be 45º, and that's quite a pullout.

In this instance, surely the load on each anchor is much reduced (halved?).

Not being a scientist, merely a humble caver, I would think that testing in the direction of use, rather than pull out would be a more pertinent test.

Just out of interest, are there any actual instances of eco anchors pulling out underground? ( I don't mean like on the second pitch in Knotlow, where most of the wall the anchor was attached to disappeared down the pitch some years ago).

 

[nickwilliams]

In this instance, surely the load on each anchor is much reduced (halved?).

Not necessarily. It's all dependent on the angle of the rope. Hopefully someone with more time will be along shortly to explain the detail (or point you to somewhere else you can find it on line) but you should know that with a 'Y' hang it is perfectly possible (although admittedly unlikely) to actually apply more load to each anchor than would be applied to only a single bolt.

Not being a scientist, merely a humble caver, I would think that testing in the direction of use, rather than pull out would be a more pertinent test.

There's a need for a compromise here, because applying large radial loads to an anchor in a real cave setting is actually quite difficult to achieve (and would in many cases require extra anchors specifically placed in order to perform the tests). In practice, so long as it is placed in competent rock the anchor will be weakest when loaded axially (this is both common sense and also fairly easy to prove experimentally).

It's important to remember that there is a difference between testing an anchor to destruction in order to understand how strong it is and what the failure modes are, and proof loading it in order to give an indication that it continues to be safe to use. The only way one can unequivocally identify the strength of any given anchor is to load it until it breaks. Obviously it then can't be used again! The purpose of a proof load it to apply a test which gives an indication that the anchor is in fact strong enough and will continue to be so until the next test. The selection of the load used during a proof test is based on a number of factors. Ideally the force will be greater than the normal working load placed on the anchor since this will provide a high degree of confidence that the anchor continues to be safe to use but it doesn't 'prove' that it will be safe until the next time it is tested, or indeed, that it will be safe if there is an unexpected overload applied such as might be generated in a fall.

So, the load and method of proof loading will always be a compromise between the need to load the anchor enough to actually provide a meaningful result (but not cause it any damage which will weaken it) and the actual practicality of applying the test in a way which can produce repeatable results.

Experience  to date indicates that a test which applies only an axial load nevertheless gives an acceptably high degree of confidence that the anchor is safe to use even though in use the anchor may be loaded differently in actual use. Given the difficulty of applying a radial load and the fact that (in the context of a regular proof load) it would not appear to give us very much useful additional information, currently we don't do one, but Jopo is correct to say that this is something which should be reviewed regularly.

Nick.

(modified with the addition of the last paragraph)

 

[nickwilliams]

(grr, damn thing apeared twice!)

 

[nickwilliams]

(grr, damn thing appeared twice!)

 

[spikey]

Thanks for that Nick - as I said, I'm not au fait with the physics of the issue.

I repeat the original question however. We are all aware of the number of spit failures which have occured over the years, but has an eco anchor yet failed in practice (ie. whilst being used underground)?

 

[Cave_Troll]

the famous one is on the second pitch of Knotlow in derbyshire.
The bolt was placed but the chunk of rock it was placed in came out.
There is now a rock the size of a small TV at the bottom of the pitch with a bent Panchor in it.

having been given the job of removing P anchors i can testify that they can be buggers to get out even when the resin bond to the rock has failed.

 

[cap n chris]

Just out of interest, are there any actual instances of eco anchors pulling out underground? ( I don't mean like on the second pitch in Knotlow, where most of the wall the anchor was attached to disappeared down the pitch some years ago).

 

[Cave_Troll]

sorry i replied to his repost and so didn't see the first post.

I don't think inserting bolts into walls by banging htem in with your head is a recognise technique

 

[wormster]

I don't think inserting bolts into walls by banging htem in with your head is a recognise technique

HAHAHAHAHAHA

how about jumping on then then:

 

[Peter Burgess]

Is this better?

 

[Cave_Troll]

ah happy memories of drilling holes at full stretch while hanging off a rope

 

[cap n chris]

Is this better?

 

[spikey]

the famous one is on the second pitch of Knotlow in derbyshire.

Yeah, I mentioned this one in my original post, I just wondered if there were others. There seems to have been a modicum of concern about rotational movement of certain eco hangers (see the Rhino Rift thread, in the Mendip section), and I was interested as to whether any had actually failed.

 

[wormster]

Yeah, I mentioned this one in my original post, I just wondered if there were others. There seems to have been a modicum of concern about rotational movement of certain eco hangers (see the Rhino Rift thread, in the Mendip section), and I was interested as to whether any had actually failed.

Went down Rhino at the weekend, no loose p hangers that I noticed, But the plate hanger on the 2nd? pitch does swivel a bit, but it ain't loose.

 

[cap n chris]

Many of the bolts in Rhino exhibit (acceptable) slight rotational movement; the "plate hanger" isn't part of the rig so is irrelevant. For those who are new to this topic there's a huge long thread on the RR bolts BTW, here http://ukcaving.com/board/index.php/topic,3220.0.html

 

[wormster]

All the bolts in Rhino exhibit (acceptable) slight rotational movement; the "plate hanger" isn't part of the rig so is irrelevant. For those who are new to this topic there's a huge long thread on the RR bolts BTW, here http://ukcaving.com/board/index.php/topic,3220.0.html

Thanks for the info C 'n C

 

[cap n chris]

You're welcome; glad to be of assistance.  :hug:


Note: changed "all" to "many".