Author Topic: What throughbolt?  (Read 2856 times)

Offline SamT

  • Global Moderator
  • forum hero
  • *****
  • Posts: 6379
    • The Eldon Pothole Club
Re: What throughbolt?
« Reply #50 on: November 24, 2020, 10:47:53 am »
Yeah - in this vid, they use a normal treaded extractor.


UK Caving

Re: What throughbolt?
« Reply #50 on: November 24, 2020, 10:47:53 am »
Warmbac

Online pwhole

  • forum hero
  • *****
  • Posts: 2356
  • TSG, DCA, PDMHS
    • Phil Wolstenholme website
Re: What throughbolt?
« Reply #51 on: November 24, 2020, 11:39:00 am »
One point to bear in mind though is that whilst the first video is very impressive, he's working in a nice boulder on the floor outdoors. A wet vertical pitch with three rebelays to deal with may make much of that job considerably more difficult! Though I can see by his little wire loops on the spacers that he has thought about that aspect.

My other concern, which the guy doesn't mention, is the installation stress. As throughbolts are an expansion fit, the rock around it must be compaction-stressed for it to work. Does this removal method then 'relax' the stress again? I know steel is very elastic, albeit not usually on scales we can easily appreciate - although over-tightened concrete screws slightly unscrewing over time is a good practical example here - but I don't think rock is elastic at all, especially limestone. I would guess that the expansion of the cone when first installed could set up a permanent stress force that could only be relieved by crystal/grain failure. A bit like explosive slickensides being released by a drill or pick. So even if you installed a resin anchor could you completely rely on it? A pull-test on the fixing bond wouldn't test the strength of the surrounding rock as that would need to be a shear load. And it may take several shear loads (i.e. people) before it fails.

Offline andrewmc

  • BCA ind. rep.
  • junky
  • ****
  • Posts: 974
  • EUSS, BEC, YSS, SWCC...
Re: What throughbolt?
« Reply #52 on: November 24, 2020, 03:55:34 pm »
My other concern, which the guy doesn't mention, is the installation stress. As throughbolts are an expansion fit, the rock around it must be compaction-stressed for it to work. Does this removal method then 'relax' the stress again? I know steel is very elastic, albeit not usually on scales we can easily appreciate - although over-tightened concrete screws slightly unscrewing over time is a good practical example here - but I don't think rock is elastic at all, especially limestone.

This paper https://www.sciencedirect.com/science/article/abs/pii/0148906272900472 (of which I can only see the abstract) says: 'Deformation under conditions of uniaxial strain was found elsewhere to be very nearly recoverable for rocks like granite, diabase and certain limestones.' which would suggest that at least for 'certain limestones' the rock is pretty elastic.

I would assume the hole might be buggered from crushing the edges into dust or fracturing it, but generally limestone seems pretty brittle to me, which would suggest it is pretty elastic? I wouldn't want to put another throughbolt in the same hole (at least not the same size) but would be happier replacing say an 8mm bolt with a 10mm or 12mm throughbolt, or a 12mm or 16mm resin. But I have no testing to back this up, and would prefer not to...

Hopefully a real geoengineer can tell me my intuition isn't completely wrong that there wouldn't be much of a stress cone left in the rock after the stress (from the tightened through-bolt) is removed.

I'm probably horribly misreading this paper: http://english.gyig.cas.cn/pu/papers_CJG/201803/P020180316540678877346.pdf
but Fig 2 to me suggests it's probably fairly elastic for a few hundred MPa stress; by comparison I just saw a figure of 400MPa for the yield strength of a 5.8 carbon steel bolt.

Offline JB35

  • Newbie
  • *
  • Posts: 2
Re: What throughbolt?
« Reply #53 on: November 24, 2020, 05:34:42 pm »
I agree (also not a geoengineer). I would imagine the plastic region of limestone is going to be pretty small before fracture and any localised deformation at the bolt is actually just digging in and fracturing the rock, much less deforming it.  Even then, surely if the stress concern is caused by placing the bolt rather than removing it, then the logical conclusion is that every through-bolt placement in use is in weakened rock and also questionable?

I have wondered whether there would be a significant strength reduction when placing a through-bolt in a hole which has previously had a concrete screw placed in it. I would guess the results of any tests would deviate massively depending on whether the thread or sleeve lined up.

A bit off-topic, but I would have thought that on the larger scale there exists a significant amount of stress on most bits of rock. After all, it's got a fair amount of rock tonnage weighing down on it. I would like to hope that bolts don't get any more dangerous the deeper you go!

Offline SamT

  • Global Moderator
  • forum hero
  • *****
  • Posts: 6379
    • The Eldon Pothole Club
Re: What throughbolt?
« Reply #54 on: November 24, 2020, 09:38:04 pm »
One point to bear in mind though is that whilst the first video is very impressive, he's working in a nice boulder on the floor outdoors. A wet vertical pitch with three rebelays to deal with may make much of that job considerably more difficult! Though I can see by his little wire loops on the spacers that he has thought about that aspect.

My other concern, which the guy doesn't mention, is the installation stress. As throughbolts are an expansion fit, the rock around it must be compaction-stressed for it to work. Does this removal method then 'relax' the stress again? I know steel is very elastic, albeit not usually on scales we can easily appreciate - although over-tightened concrete screws slightly unscrewing over time is a good practical example here - but I don't think rock is elastic at all, especially limestone. I would guess that the expansion of the cone when first installed could set up a permanent stress force that could only be relieved by crystal/grain failure. A bit like explosive slickensides being released by a drill or pick. So even if you installed a resin anchor could you completely rely on it? A pull-test on the fixing bond wouldn't test the strength of the surrounding rock as that would need to be a shear load. And it may take several shear loads (i.e. people) before it fails.

I'll go back to my earlier point about worrying too much over certain aspects of this.  So bogged down are we, in the minutia of detail, that I think we forget to take a step back a bit and look at the bigger picture i.e. the fact that other than resin/rock bond failure, or massive rock integrity failure (putting your bolt in loose block), THE THINGS JUST AREN'T BLOODY EVER GOING TO COME OUT!!.

Even the ones that have visibly moved (rock/resin bond failure) that I've replace took enormous amounts of drilling effort and hydraulic pullers pulling axially to get the damned things out.

Anyway - we all digress.


Offline SamT

  • Global Moderator
  • forum hero
  • *****
  • Posts: 6379
    • The Eldon Pothole Club
Re: What throughbolt?
« Reply #55 on: November 24, 2020, 09:40:33 pm »
One point to bear in mind though is that whilst the first video is very impressive, he's working in a nice boulder on the floor outdoors. A wet vertical pitch with three re-belays to deal with may make much of that job considerably more difficult! Though I can see by his little wire loops on the spacers that he has thought about that aspect.


OK - some folks doing it dangling on ropes...



albeit on a nice sunny day.   (I do like the look of his puller mind, very swish)

Offline Joel Corrigan

  • obsessive maniac
  • ***
  • Posts: 337
    • Skytek Ltd
Re: What throughbolt?
« Reply #56 on: November 25, 2020, 03:09:55 pm »
Hmmmn, not sure I completely agree, SamT, as I've certainly had a few bolts pop on me over the years so it's absolutely possible.  Top of my head: a Spit pulled out on Beardy down the Scialet de la Fromagere (a non-caver reading this thread would wonder what sort of kinky shit we get up to!!), a thru-bolt popped on Martin Groves in the Dachstein, and I've had more than a couple go on me but the only place that I remember was in Papua New Guinea & I think the issue there was that it was relatively soft & friable karst so we probably needed long thru-bolts with double sleeves.  Saying that, I get your point about getting bogged down in the irrelevant micro-details, though... 

The ease of bolting with battery drills has meant that somewhere along the line the caving world has down-skilled as a lot of the current batch of riggers have missed out on learning some of the fundamentals as poor skills get passed along the chain.  We used to have a policy in Austria whereby nobody was allowed to touch a battery drill until they'd done at least two years of hand bolting & that produced some capable explorers.  Sadly, that's not been a thing for quite a while which is a shame ;-/   

Offline nobrotson

  • Wob Rotson, ULSA
  • stalker
  • ***
  • Posts: 258
  • This not bono. Why the plastic fruit?
Re: What throughbolt?
« Reply #57 on: November 25, 2020, 05:03:40 pm »
The ease of bolting with battery drills has meant that somewhere along the line the caving world has down-skilled as a lot of the current batch of riggers have missed out on learning some of the fundamentals as poor skills get passed along the chain.  We used to have a policy in Austria whereby nobody was allowed to touch a battery drill until they'd done at least two years of hand bolting & that produced some capable explorers.  Sadly, that's not been a thing for quite a while which is a shame ;-/

Explains why it took you so long to find that connection if you stopped everyone using drills.

But seriously, what key bolting skills do you think don't get passed on if someone is taught using a drill as opposed to hand bolting? I have a lot of respect for people with good handbolting skills and caved with some Austrians who could place spits by hand about as quickly as some people I've caved with could do with a drill. I will openly admit I'm not very good at it; I remember taking ages to tick off some poor surface leads in Austria (not the Dachstein) with hand bolts when I'd just started alpine caving. But I don't really see what you miss out on by jumping straight to bolting with a drill, apart from maybe not choosing your placements carefully enough since it's too easy to whack another anchor in?
the man is mentally ill. I have seen him eat a plastic pie.

Offline Fjell

  • obsessive maniac
  • ***
  • Posts: 355
Re: What throughbolt?
« Reply #58 on: November 25, 2020, 05:04:55 pm »
The setting torque for a 8mm bolt is something like 15 Nm. That is about 10kg on a 15cm spanner and would induce about 1000kg of tension (preload). I would suggest that isn’t coming out any time soon.

If you can’t generate that torque then the placement is a dud. If after a few prussiks there is no torque, the placement is a dud. If that keeps happening you have the wrong fastener for the situation and some pencil sharpening is required. For hopefully obvious reasons you should not use a fastener unless you can meet the installation criteria. Give Hilti et al a break, they put a lot of effort into it.

Spits are seen as suitable by Hilti for things like cable trays with loads realistically far below the nominal strength. They were about the only convenient option many moons ago, but that has passed with Li-ion batteries and drills. They can’t be load-tested prior to use unless you bring a machine and are very shallow. I always viewed vertical placements as somewhat heroic in nature.

Offline Steve Clark

  • Newbie
  • *
  • Posts: 25
Re: What throughbolt?
« Reply #59 on: November 25, 2020, 09:49:32 pm »
I did speak to Hilti today. There isn't much discount routinely available on those top of the range fancy stainless HST-HCR bolts :

HST-HCR M8x75mm - 12.00+VAT (each)
HST-HCR M8x115mm - 14.50+VAT (each)

Boxes of 50

Prices valid until Brexit. lol.

Offline SamT

  • Global Moderator
  • forum hero
  • *****
  • Posts: 6379
    • The Eldon Pothole Club
Re: What throughbolt?
« Reply #60 on: November 26, 2020, 09:02:04 am »
Hmmmn, not sure I completely agree, SamT, as I've certainly had a few bolts pop on me over the years so it's absolutely possible.  Top of my head: a Spit pulled out on Beardy down the Scialet de la Fromagere (a non-caver reading this thread would wonder what sort of kinky shit we get up to!!), a thru-bolt popped on Martin Groves in the Dachstein, and I've had more than a couple go on me but the only place that I remember was in Papua New Guinea & I think the issue there was that it was relatively soft & friable karst so we probably needed long thru-bolts with double sleeves.  Saying that, I get your point about getting bogged down in the irrelevant micro-details, though... 


I was thinking more with regards to resin bolts, not through bolts.  Yes, I can imagine spits  pulling quite easily, (not happened to me) and I've placed some pretty shonky short through bolts in crap rock on occasion.

I think the topic was extracting a through bolt, to re-drill with a bigger hole, to presumably place a resin anchor, and phil expressed concern about the 'pre stressed' state of the limestone, which is I think over thinking it. 

That whole 'stressed' rock thing comes from days gone by when spits were (re)placed in near proximity on popular pitch heads.   Since the area of stress is very close to the surface with a spit, then you could get 'dinner plating' of the rock.  However, at the depth of through bolts and certainly resin anchors, I just cant see an issue and the replacement resin anchor is (if correctly installed) going to be utterly bombproof in comparison. 

Even on those videos, where people are pulling through bolts, sometimes without doing the spinning trick, there is very little or no scabbing of the rock. (clearly the quality of the rock is a factor here)

Offline Joel Corrigan

  • obsessive maniac
  • ***
  • Posts: 337
    • Skytek Ltd
Re: What throughbolt?
« Reply #61 on: November 26, 2020, 01:49:58 pm »
The ease of bolting with battery drills has meant that somewhere along the line the caving world has down-skilled as a lot of the current batch of riggers have missed out on learning some of the fundamentals as poor skills get passed along the chain.  We used to have a policy in Austria whereby nobody was allowed to touch a battery drill until they'd done at least two years of hand bolting & that produced some capable explorers.  Sadly, that's not been a thing for quite a while which is a shame ;-/

Explains why it took you so long to find that connection if you stopped everyone using drills.

But seriously, what key bolting skills do you think don't get passed on if someone is taught using a drill as opposed to hand bolting? I have a lot of respect for people with good handbolting skills and caved with some Austrians who could place spits by hand about as quickly as some people I've caved with could do with a drill. I will openly admit I'm not very good at it; I remember taking ages to tick off some poor surface leads in Austria (not the Dachstein) with hand bolts when I'd just started alpine caving. But I don't really see what you miss out on by jumping straight to bolting with a drill, apart from maybe not choosing your placements carefully enough since it's too easy to whack another anchor in?

You youngsters are far too cheeky, Rob!  This is obviously far away from Ari's original post but I'll try to justify my sweeping statement although my brain is struggling a bit today.  A few major changes happened in the rigging game during my time & I saw the effect that it had on subsequent generations of cavers. 

1), When I started, Spits were the standard anchor & just learning to rig ropes down already-explored caves was a challenge as a lot of the time you had to search for the little buggers.  This meant that as a newbie I had to really think about where the original explorer would have placed the bolts in order to find them which meant that I was subconsciously self-training myself for the time when I'd be placing my own anchors.  I'm not explaining myself very well but the huge difference today is that you can just drop down a hole & join the dots without having to put any thought into it & the result is that pretty much anyone can rig SRT routes without necessarily understanding the principles. 

2), Placing anchors was also a challenge that required thought, fitness, and some skill.  Our Baby-Rigger soon learned that in a cold cave with absurdly hard limestone that proper placement was vital as he may only have the energy to install a couple of bolts before his arm fell off or his legs went numb so he had to make them count, and because installing fancy traverses etc... wasn't necessarily an option he'd have to choose his spot wisely.   

3), Because hand-bolting was difficult & time-consuming, our "pre-battery" rigger also learned a host of other rigging skills to help him along the way.  These included the use of pegs, wires, naturals etc... that aren't very common nowadays because battery drills are so convenient.   

Don't get me wrong: I'm obviously a massive fan of battery-powered tools but I will also make sure that I have a Spit Driver with me for the initial preparation/cleaning of the rock & if the batteries die then I will also be able to install a Spit by hand in order to finish the route off, escape etc...  That could make a difference between having just a bad day at the office & a nightmare for some. 

I just feel that in order to be a "complete" rigger that some of these skills shouldn't necessarily be abandoned & I've observed a massive difference in skill levels since the rise of the ring hanger.       

       


 

Main Menu

Forum Home Help Search
SimplePortal 2.3.5 © 2008-2012, SimplePortal