Bolt failures

Jon

Member
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?
 

Wolfo

Member
You can f*** 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 f*** 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).
 

Stu

Active member
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.
 

langcliffe

Well-known member
Jon said:
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!
 

andrewmcleod

Well-known member
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'.
 

mikem

Well-known member
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)...
 

Bob Mehew

Well-known member
Jon said:
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/ .


 

Hammy

Member
https://ukcaving.com/board/index.php?topic=3697.0

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

Simon Wilson

New member
Jon said:
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.

Jon said:
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.
 

Simon Wilson

New member
Bob Mehew said:
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.

https://youtu.be/2PO7-yUJ_FQ

Bob Mehew said:
A few were replaced.

A lot more than a few have been replaced.
 

caving_fox

Active member
langcliffe said:
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.
 

Simon Wilson

New member
Ian Ball said:
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
 

Fulk

Well-known member
Simon Wilson:
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).
 

paul

Moderator
caving_fox said:
langcliffe said:
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?
 

caving_fox

Active member
paul said:
caving_fox said:
langcliffe said:
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?

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