What throughbolt?
- Thread starter aricooperdavis
- Start date
Pitlamp
Well-known member
Um - I think I'll just have to try this and see what happens.
It was me that placed this particular bolt (not in one of our popular caves) and I always over-drill the holes, for reasons which other folk have given above. So the default option is to hammer in flush with the rock. But I'd prefer to extract the bolt so the hole may be used again. (I guess part of this is that I was wanting to show it can be done, providing an example which I hoped others might then follow. I'm trying to factor in conservation here.)
Another option might be to pull the bolt out using the curved end of a bog horse's head bar, with a packing piece under the curved bit to position it to maximum advantage. (a bit like removing a nail with a claw hammer.)
It was me that placed this particular bolt (not in one of our popular caves) and I always over-drill the holes, for reasons which other folk have given above. So the default option is to hammer in flush with the rock. But I'd prefer to extract the bolt so the hole may be used again. (I guess part of this is that I was wanting to show it can be done, providing an example which I hoped others might then follow. I'm trying to factor in conservation here.)
Another option might be to pull the bolt out using the curved end of a bog horse's head bar, with a packing piece under the curved bit to position it to maximum advantage. (a bit like removing a nail with a claw hammer.)
Pitlamp
Well-known member
Thanks for the video links Sam - interesting. The key thing seems to be to wear down a lip on the cone shaped end so the sleeve doesn't travel / tighten whilst the anchor is being extracted. Might have a play some time using an old car jack which sometimes gets used for shifting boulders.
Or - maybe Simon Wilson will see this and hopefully share his experiences? (Thanks for mentioning this MarkS.)
Or - maybe Simon Wilson will see this and hopefully share his experiences? (Thanks for mentioning this MarkS.)
SamT
Moderator
MarkS said:
I agree, but Pitlamp was asking for a technique for one particular placement, already installed.
No evidence of Simon having removed one of those type of sleeved through bolts on his page. Lots of very similar videos online from the states using the same technique, generally looks pretty straight forward and successful. I think the key is probably the hydraulic puller they are using and also using something that you can 'pull' up on, whilst spinning the bolt. i.e. just a socket spinning the bolt isn't going to allow you to pull up on the bolt which is what causes the requisite groove to be cut in the cone.
SamT said:
For spits we made up something like a bearing puller. The centre bolt had a hole drilled trough it so we could tap the cone while giving it a gentle pull. You wouldn't need the centre hole for a throughbolt but the simple puller design should work without taking some fancy hydraulic thing into a world of mud and grit.
pwhole
Well-known member
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.
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.
andrewmcleod
Well-known member
pwhole said:
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.
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!
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!
SamT
Moderator
pwhole said:
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.
Joel Corrigan
New member
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 ;-/
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 ;-/
nobrotson
Active member
Joel Corrigan said:
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 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.
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.
Steve Clark
Well-known member
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.
HST-HCR M8x75mm - 12.00+VAT (each)
HST-HCR M8x115mm - 14.50+VAT (each)
Boxes of 50
Prices valid until Brexit. lol.