Author Topic: Bolt failures  (Read 1163 times)

Offline Jon

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Bolt failures
« on: February 16, 2019, 06:36:58 pm »
I try to rig with best practice in mind, one of the considerations being a bolt failure. Am I correct in assuming that P bolt failures are rare or non existent, through bolt failures are rare but spit failures occurred enough to warrant the move to P bolts?

With P bolts and through bolts, is it more common for the rock to fail rather than the bolt pull out, which suggests poor placement?

Offline Wolfo

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Re: Bolt failures
« Reply #1 on: February 16, 2019, 07:11:04 pm »
You can fuck up any bolt, wether Spit, P_Bolt or Hilti by bad placement or bad luck.
If the "death solid" rock you pound/glue the anchor in, decides to burst off one day...that could happen, seldom, but it happend in the past.

The P_bolts are nearly resistent against corrosion (a big problem with SPITs, never trust an old one!) and the max. allowable loads are much higher - but you could easily fuck up the glue or cement, so placement of P_bolts is a process with needs some care and special knowledge.
Mechanical heavy duty anchors (Hilti etc.) in the stainless edition are also pretty tought, almost same as the p_bolts - and much easier to install and controll in the point of correct fitment. But they are much more expensive and need a more carefull look at the rock you may want to drill your bolt hole into (the mechanical "lock" stresses the rock with some force, so it should be compact around the placement point).
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Offline Stuart Anderson

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Re: Bolt failures
« Reply #2 on: February 16, 2019, 07:15:48 pm »
I think practically to, that the constant screwing in and out damaged many Spits, hence the bolt rash in some caves. Threads get damaged etc so a more permanent solution was sought.
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Offline andrewmc

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Re: Bolt failures
« Reply #3 on: February 16, 2019, 07:19:49 pm »
Rig like any bolt/anchor could fail.

Offline Jon

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Re: Bolt failures
« Reply #4 on: February 16, 2019, 07:23:14 pm »
Rig like any bolt/anchor could fail.
I mentioned that in my post, I just want some history \ context about bolt failures.

Offline langcliffe

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Re: Bolt failures
« Reply #5 on: February 16, 2019, 07:26:28 pm »
With P bolts and through bolts, is it more common for the rock to fail rather than the bolt pull out, which suggests poor placement?

There have been problems with P-hangers installed by untrained people where the resin hasn't set (not CNCC hangers).

A substantial part of the wall on the bottom pitch of Little Hull Pot which had a deviation P-hanger became detached and finished up at the bottom of the shaft. I wouldn't like to say that it was poor placement, however. Although the shaft is in a fault and the rock is inherently fractured, I would never have envisaged a whole chunk of the wall peeling off if I had been bolting it. The P-bolt was still standing firm and proud in the rock, only at the bottom of the pitch!

I have never known a P-hanger fail. I remember that Mike Wooding and I removed a 'dangerously loose"one on GG Main Shaft, and it took something like two hours!

Offline andrewmc

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Re: Bolt failures
« Reply #6 on: February 16, 2019, 08:02:09 pm »
One of the nice things about the BP anchors is that if you still the right size hole (and don't ream it out like I think some people have) then the anchor is often still plenty strong enough _even without resin_ as it is a tight interference fit, and pulling down on the bolt causes it to change shape slightly and jam in anyway.

My point was that once you have decided what the 'safe enough' anchors are there is little to no point worrying about 'how' safe. Only with the worst of spits would I consider backing up a Y-hang, for example, and probably only because I had decided the spit was too bad to 'count'.

Offline mikem

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Re: Bolt failures
« Reply #7 on: February 16, 2019, 08:11:01 pm »
Spits also spread the load over a very small "cone" area of rock & had people doing them up to various degrees of tightness. Whilst, as Andrew says, a p bolt is quite difficult to remove even if it isn't glued in. But whilst a spit is quite easy to inspect & decide whether you want to use it, you can't see what is going on with a p bolt & at some point some will deteriorate to the point where they need replacing, we just don't know when that will be (others may well last for ever if there's nothing to react with)...

Offline Bob Mehew

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Re: Bolt failures
« Reply #8 on: February 16, 2019, 09:46:03 pm »
I just want some history \ context about bolt failures.

With the first few uses of SRT it quickly became apparent that one needed to obtain better hangs than could be obtained using natural belay points due to rope rub. So anchors were placed.  A popular version was the spit which required you to take your own hanger and bolt to screw into each placed spit.  (Plus in the pre electric drill days, spits were simple to place with just a hammer.)  As I recall, a book was written on a set of popular routes using red headed spits.  The problem then arose with the popularity of these routes, when cavers using dirty threads on their bolts, the thread in the spit became unusable.  That lead to other spits being placed near by hence giving rise to a rash of spits. 

Les Sykes, Glenn Jones and others sought a way around this problem and with the help of a Hilti rep found in the early 90s the DMM Eco anchor together with a resin would work in cave.  The technique was 'exported' to other regions and adopted by the then National Caving Association (NCA).  The technique was handed onto BCA. 

In the mid 2000's DMM gave up making Eco anchors.  After a fair amount of effort by Les and others, the Bolt Product (BP) resin anchor was chosen as a replacement.  However, the twisted legs of a BP anchor fill the hole in the rock.  When there was a question over an installed Eco anchor, one could just drill down each side of the straight legs mostly within the resin and get sufficient reduction in strength that one could then extract the Eco anchor albeit with some effort.  There is still an unproven concern that a BP anchor will require a larger hole which is worrying on the basis of conservation of belay points.  So Simon Wilson came up with the IC anchor.  There has also been a suggestion to use titanium anchors but the experience has been mixed and that is disregarding their price.

There has been changes in the resin used over the years and yes there has been a number of concerns raised over certain anchor being loose.  In a fair number of cases the concern was due to the person failing to take a true measure of movement, instead sensing from the movement of their fingers that the bolt was loose, rather than that their fingers were flexing.  A few were replaced.

If you think an anchor is loose, then please report it ASAP to your regional caving council.

It is worth noting that the bonding of a resin anchor is not just based on the chemical bond of surface of resin to rock and resin to anchor but also on the mechanical interaction of the resin with the features of the anchor and also with the irregularity of the hole in the rock.  (You do not use diamond drills to place anchors!)

Eco, BP and IC anchors are made from 316 Stainless Steel (SS).  That was chosen to avoid the potential for Chloride Stress Corrosion Cracking (CSCC - not the region) in UK caves.  However there have been a few cases in high temperature countries where SS bolts on sea cliff climbs have cracked.  There has also been a case or two where poorly welded SS anchors have cracked under what is thought to be CSCC.  There was one case in the UK where the location was found to be flow stone over mud over rock - so the surface flow stone cracked when it was tested. 

There is a large amount of information at https://cncc.org.uk/fixed-aids/ , http://british-caving.org.uk/wiki3/doku.php?id=equipment_techniques:anchor_scheme and https://www.thebmc.co.uk/articles/tag/bolt%20technical .  Simon also reported his work at http://www.resinanchor.co.uk/ .


 

Offline Hammy

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Re: Bolt failures
« Reply #9 on: February 16, 2019, 10:03:47 pm »
https://ukcaving.com/board/index.php?topic=3697.0

Yes here is an example of a resin bolt failure in Rhino Rift

Offline Hammy

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Re: Bolt failures
« Reply #10 on: February 16, 2019, 10:05:39 pm »
https://ukcaving.com/board/index.php/topic,3221.0.html

And here is the thread that preceded it...

Offline Simon Wilson

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Re: Bolt failures
« Reply #11 on: February 17, 2019, 05:17:13 pm »
I try to rig with best practice in mind, one of the considerations being a bolt failure. Am I correct in assuming that P bolt failures are rare or non existent, through bolt failures are rare but spit failures occurred enough to warrant the move to P bolts?

Correct. The well-known Rowten accident caused very serious injury and resulted in much effort to prevent any more Spits being installed. Anecdotally there have been a considerable number of accidents when Spits failed.


With P bolts and through bolts, is it more common for the rock to fail rather than the bolt pull out, which suggests poor placement?

Correct on both counts.
See Langcliffe above. When I was removing a non-CNCC resin anchor from a Dales cave a slab of rock came away with the anchor in it.

Offline Simon Wilson

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Re: Bolt failures
« Reply #12 on: February 17, 2019, 05:52:19 pm »

There has been changes in the resin used over the years and yes there has been a number of concerns raised over certain anchor being loose.  In a fair number of cases the concern was due to the person failing to take a true measure of movement, instead sensing from the movement of their fingers that the bolt was loose, rather than that their fingers were flexing. 


The CNCC have had a "fair number" of loose anchors reported since we started asking people to report them and in every case the reported loose anchors showed significant movement.

Thanks for your reports folks.

I don't think anybody can fail to recognise a loose anchor.




A few were replaced.


A lot more than a few have been replaced.

Offline Ian Ball

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Re: Bolt failures
« Reply #13 on: February 17, 2019, 06:16:33 pm »
Please could I ask when installation practice included sinking the head of the p into a drilled groove?

Offline Simon Wilson

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Re: Bolt failures
« Reply #14 on: February 17, 2019, 06:34:30 pm »
1994.

Offline caving_fox

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Re: Bolt failures
« Reply #15 on: February 18, 2019, 09:18:04 am »

A substantial part of the wall on the bottom pitch of Little Hull Pot which had a deviation P-hanger became detached and finished up at the bottom of the shaft. I wouldn't like to say that it was poor placement, however. Although the shaft is in a fault and the rock is inherently fractured, I would never have envisaged a whole chunk of the wall peeling off if I had been bolting it. The P-bolt was still standing firm and proud in the rock, only at the bottom of the pitch!


There's a small block at the bottom of an Oxlow pitch with a proud P bolt too. At the pitch head you're wishing for another bolt somewhere, and it's only when you get to the bottom that you find it. It's a cube of rock, a foot or so a side that failed.
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Offline Simon Wilson

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Re: Bolt failures
« Reply #16 on: February 18, 2019, 09:53:04 am »
Please could I ask when installation practice included sinking the head of the p into a drilled groove?

I just checked the minutes and it was in 1995 that the CNCC Rep reported to the E&T that they were countersinking anchors. I think I'm correct in saying that it was in 1994 that countersinking started to be done by at least some installers.

Apparently this was to prevent loose anchors rotating. When I first turned my attention to the problem of loose anchors I wanted to find out why they were coming loose in order to be able to prevent them coming loose at all.

You can read the E&T minutes here: http://british-caving.org.uk/wiki3/doku.php?id=equipment_techniques:meetings

Offline Fulk

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Re: Bolt failures
« Reply #17 on: February 18, 2019, 11:15:11 am »
Simon Wilson:
Quote
Anecdotally there have been a considerable number of accidents when Spits failed.

Here's another anecdote: Back in 2008 I had two bolts pop out of Spits in two trips in one week (though neither caused an accident).

Offline paul

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Re: Bolt failures
« Reply #18 on: February 18, 2019, 11:51:03 am »

A substantial part of the wall on the bottom pitch of Little Hull Pot which had a deviation P-hanger became detached and finished up at the bottom of the shaft. I wouldn't like to say that it was poor placement, however. Although the shaft is in a fault and the rock is inherently fractured, I would never have envisaged a whole chunk of the wall peeling off if I had been bolting it. The P-bolt was still standing firm and proud in the rock, only at the bottom of the pitch!


There's a small block at the bottom of an Oxlow pitch with a proud P bolt too. At the pitch head you're wishing for another bolt somewhere, and it's only when you get to the bottom that you find it. It's a cube of rock, a foot or so a side that failed.

Are you sure you're not thinking or Perl Chamber in Knotlow Cavern?
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Offline caving_fox

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Re: Bolt failures
« Reply #19 on: February 19, 2019, 10:48:07 am »

A substantial part of the wall on the bottom pitch of Little Hull Pot which had a deviation P-hanger became detached and finished up at the bottom of the shaft. I wouldn't like to say that it was poor placement, however. Although the shaft is in a fault and the rock is inherently fractured, I would never have envisaged a whole chunk of the wall peeling off if I had been bolting it. The P-bolt was still standing firm and proud in the rock, only at the bottom of the pitch!


There's a small block at the bottom of an Oxlow pitch with a proud P bolt too. At the pitch head you're wishing for another bolt somewhere, and it's only when you get to the bottom that you find it. It's a cube of rock, a foot or so a side that failed.

Are you sure you're not thinking or Perl Chamber in Knotlow Cavern?

  :clap2: that'll be the one. Didn't know the chamber had a name.
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