Bolting

[Bob Mehew]

In the 15 plus years I have been involved with E&T committee, bolting in mines is something E&T has never got to grips with.  (There was Gethin's work & some done in Devon & Cornwall, but the main focus has been on limestone.)  I would list the major areas not yet answered are:

    a) the different rock type and its bedding (or cleavage) patterns,
    b) inbuilt rock stresses induced by blasting, and
    c) corrosion due to water contaminated by minerals. 

The nearest E&T got to considering the topic was a comment which came from Cornwall of using an easily extractable throughbolts and removing them between trips to minimise corrosion.  But that just deals with the heightened corrosion problem.  And no doubt there could be other areas needing consideration.

 

[sinker]

As a absolute novice in srt  may some one send me a link to a picture of the bolts some people are saying are bad ? So I can check if I ever see any please 

There are hundreds of different types / sizes / materials etc but typically they look like this:

https://www.screwfix.com/p/easyfix-bright-zinc-plated-carbon-steel-concrete-bolts-m10-x-100mm-10-pack/5800P?tc=CA8&ds_kid=92700048793290424&ds_rl=1249413&gclid=EAIaIQobChMIzOLTubqC8AIVi9d3Ch19zAJpEAQYBCABEgKW_vD_BwE&gclsrc=aw.ds

!!! AVOID !!!

 

[Fishes]

I use concrete screws are a temporary solution. If it doesn't go then I take them out and they can be used again. If it goes then I take them out and put in fixed stainless steel anchors. That's my personal choice as they can take a lot more loading than my body and I never hang on only one bolt of any type. You won't shear them off if you use the appropriate length spanner (important for many bolt types).

I choose to use then because they cause minimal damage and don't leave scrap metal littering the place.

Spits are  also useful for longer term use in certain limited conditions. These days I would only use then in places where I wouldn't want to take my drill or a Rocpec, both of which stop working if you fill them with wet gritty crap. In my experience they are generally good for 20 years or so if people don't f*** up the treads by constantly removing and replacing the anchor plates. They can be removed but its a bit of a faff.

 

[mikem]

I'm hoping some people actually mean expansion / through bolts, when they are saying concrete screws (which as sinker shows, are a different thing altogether).

If you do use concrete screws then they should be removed immediately after use, so they aren't left for others in future.

 

[tomferry]

As a absolute novice in srt  may some one send me a link to a picture of the bolts some people are saying are bad ? So I can check if I ever see any please 

There are hundreds of different types / sizes / materials etc but typically they look like this:

https://www.screwfix.com/p/easyfix-bright-zinc-plated-carbon-steel-concrete-bolts-m10-x-100mm-10-pack/5800P?tc=CA8&ds_kid=92700048793290424&ds_rl=1249413&gclid=EAIaIQobChMIzOLTubqC8AIVi9d3Ch19zAJpEAQYBCABEgKW_vD_BwE&gclsrc=aw.ds

!!! AVOID !!!

We use to use them in manholes a lot and I completely agree I have put in thousands and snapped many with socket sets nut runner guns  ! I would not  personally dangle of them  we stopped using them in manholes and switched over to the steel wall plug design with a bolt also used glass tubs of rezin in the hole when you hammer the bolt in it smashes it making it mix , with the design you have to use the air pump tool to clear out any dust though .

 

[Fishes]

I'm hoping some people actually mean expansion / through bolts, when they are saying concrete screws (which as sinker shows, are a different thing altogether).

If you do use concrete screws then they should be removed immediately after use, so they aren't left for others in future.

I am taking about concrete screws and I use them precisely because they can be easily removed. I specifically use this type - http://excaliburscrewbolts.com/products/eyebolt-8mm/  I generally use 8mm but have also used 10mm. I imagine the 6mm ones would also be useful for aid climbing. They can generally be reused several times.

I've placed hundeds of these in limestone and lifted some very large boulders on them without a problem. If I can lift around 500kg on a single bolt with a direct pull then I don't have an issue hanging off two of them. I am more concerned about the quality of rock that I'm putting them into.

 

[mikem]

Yeah, I said some people, as others, such as yourself, were obviously considering how they were using them.

 

[pwhole]

None of this is dealing with the problem of using permanent shitty cheap throughbolts for exploration that now ruin a pitch because they couldn't be removed afterwards. I ripped open my suit and my shoulder hitting a rusty throughbolt whilst prussicking up an old bolt-climb in JH, and it bled for the rest of the trip, which was filthy. Luckily I had a lump hammer in my bag and I smashed the thing off the wall - and all its compatriots. If it had happened whilst abseiling it would have been a lot worse. Of course that patch of rock is ruined now. Using permanent bolts for exploration or temporary rigging is just daft and frankly lazy. I weigh 85 kg at worst, and these things take far greater loads. I doubt whether any of the manufacturers are concerned about whether they're rated for human use as the cost of certification would far outweigh the market, and they publish strength data which we can read and make our decision based on the numbers. I always use Excaliburs as they convinced me and I like the twin-thread design.

Installing concrete screws safely is not difficult, and doesn't stress the head at all if you clean the hole out properly and give the thing a quarter-turn back before setting it just right. I often don't even use a ratchet spanner and just use a 13mm hand spanner so i can feel what's happening inside. We have some Excaliburs on the outside wall of the chapel for rigging practice and they've been there three years - I unscrewed one recenty to check it and it was completely unaltered so I screwed it back in again. Just use nylon washers to eliminate bi-metal effects. Several have been at the bottom of Longcliffe for years and are fine. I agree that once a permanent route is established then permanent stainless fixings should be installed, but up until then I don't believe we have the right to just pepper (and stress) the rock with cheap steel - it's not our land for one thing.

 

[mikem]

Probably wasn't something that they considered when installing those ones. If the hole is deeper than the length of the bolt then they can be hammered out of sight, which is preferable to leaving unwanted heads sticking out.

 

[MarkS]

Couldn't agree more, pwhole.

Sinker: Simon's work resulted in a minimum breaking load of 24 kN over 18 different concrete screws from different manufacturers and of different diameters. The consistency within samples is remarkable.

I would agree that over-tightening could certainly be dangerous, but let's remember that any anchor can be placed badly. Poorly placed throughbolts can pull a long way out before "setting", poorly placed spits can look OK but pull out easily (P49 here), overtightened/undertightened nuts/bolts on any variety of anchor can be dangerous. Even poorly mixed resin can significantly reduce the strength of resin anchors.

To get back to the OP, I think an approach that is hard to argue with is to either place something that can be removed entirely should the route be worth more than "just a look", or just place decent stainless anchors to begin with that will likely last for many decades.

 

[mikem]

& if you're not sure, then find somebody who's had more experience to take a look.

 

[pwhole]

Probably wasn't something that they considered when installing those ones. If the hole is deeper than the length of the bolt then they can be hammered out of sight, which is preferable to leaving unwanted heads sticking out.

But surely if the rock was stressed from the placement, hammering it further in isn't going to help matters much? It could even backfire years later if someone doesn't know it's there and puts another anchor too close? I know that's unlikely if a permanent route is then rigged over it, but the rock stress to me is the main reason I never use throughbolts unless they're stainless and never coming out again.

The pic below shows one problem we had that was solved by screws - this was Al starting the dig at Longcliffe, 18m down a 38m shaft, and as we didn't know whether the shaft blockage went all the way to the bottom of the shaft or was just a plug, all digging had to be done on safety ropes - for three years. As we got lower, we put new anchors in, and so on. Ironically it was full to the bottom, but we didn't know that then, and as it was NT property on CROW land, an accident would have killed the project. I would imagine I installed about 100 concrete screws over that period for various uses - abseiling, safety anchors, hauling belays etc., and they all came out again - virtually all were only used once for absolutel safety, and at 40p each it was just about viable - the only anchor left sticking out now is a bloody throughbolt someone else installed as a temporary anchor!

The other great feature of these is that they can be screwed direct into solid mineral, which would be really risky with expansions. This calcite was the hardest and toughest substance we ever encountered, but it took screws perfectly. This was a rebelay we used for a year, every weekend. I did add nylon washers shortly afterwards after I'd noticed slight rusting on another anchor with direct contact with stainless, but even that was after months.

 

[sinker]

Well you lot obviously know better that someone who has been bolting rock and concrete for 30+ years.
You're probably right, it'll probably be OK and we're probably all gifted with enough common sense to tell a bad anchor from a good one.

I've covered my arse by warning you 

 

[Fishes]

I don't have any significant experience of bolting in civil concrete. I do have 40+ years of placing bolts in limestone though.

Looking back at some of my early and inexperienced placements I would probably be quite concerned about using them now. None of my bolt placements have every failed though. I believe that placement is much more important than the type of bolt in most cases though. The only real regrets I've had are leaving behind a load of scrap metal that didn't need to be there.

As a materials scientist specialising in very technical concrete I would have concerns about putting concrete screws into certain kinds of civil concrete. That would be where you have a relatively soft matrix with a high hardness aggregate. This type of concrete seems quite common in civil construction.

 

[Mark Wright]

Well you lot obviously know better that someone who has been bolting rock and concrete for 30+ years.
You're probably right, it'll probably be OK and we're probably all gifted with enough common sense to tell a bad anchor from a good one.

I've covered my arse by warning you 

I think most of the people on this thread have well over 30+ years experience of installing mechanically and chemically bonded anchors in both recreational and industrial environments in both limestone and concrete.

I must say I was very sceptical when I first heard of the concrete screws being used for rigging. I've been installing and testing EN795 anchors in industry for the past 30+ years and using these things for hanging off didn't bear thinking about.

Henry Rockliff did a lot of testing of them in concrete at my training centre in Rotherham some years ago. I was genuinely amazed at how strong they were. I don't remember ever seeing any dynamic load test results. A 9kN dynamic force with an additional 300kg added to the dropped weight would generally be considered as being an appropriate substrate strength. They would only have to have a min 12kN BL to pass the EN795A standard and they are much stronger than that. 

I'd be interested to know if your very strong concerns haven't already been covered in the many previous threads on the subject over the years.

Remember we are not talking about what we would do in the workplace, we are talking about how best to instal a suitable anchor system when we are on a pushing trip.

If the cave doesn't go we can simply remove the anchors. If it does go then we can drill out the holes and instal resin anchors, which would be the safest possible method. Unfortunately it's not possible to rig new caves with resin anchors unless you have access to some very very very quick setting resin.

Mark

 

[mikem]

But surely if the rock was stressed from the placement, hammering it further in isn't going to help matters much?

Hitting it in will at least remove the stress, as the wedge is forced out of the sleeve (obviously doesn't work if hole is only as long as, or less than, the bolt length).

Being a big wall climber Andy Kirkpatrick also has quite a lot to say on bolts: https://www.andy-kirkpatrick.com/blog/view/hand-bolting

 

[pwhole]

Well hopefully it would release the stress, but there's no real way of checking other than with destructive testing, as putting another anchor nearby to test it out 'for failure' is obviously insane. I don't know how elastic limestone is, but I'm guessing not much - I doubt it would 'relax' again after the stress of the wedge was released. My earlier points really were to illustrate that we have thought about all this, discussed it extensively before use, and then tested the system extensively in real-world situations for literally years, both with risk and no-risk situations - with an almost zero failure rate in both, so I don't know what else we can do. No-one's suggested a superior method of temporary anchor installation yet, unless leaving unnecessary bolts everywhere can be classed as superior. Or those lovely ?40 Petzl push-button anchors, which obviously I would love to own a sackful of, but that's bolt-climbing for Arab princes, not the likes of us.

My two failures were - re-using a screw in a new hole with less-than-perfect substrate with a ratchet spanner at full extension - it got stuck, I didn't break the swarf off backwards, and snapped the head off. Second was more spectacular and entirely my fault - I'd used one for a rebelay just below the entrance pipe at Longcliffe, but hadn't noticed the rock below it was slightly fractured, and it had subsequently fallen out, leaving the bottom end of the bolt unsupported - I'd also not drilled it in perfectly perpendicular, and so it was slightly askew anyway. I abseiled onto it with my short cowstail and as soon it was fully loaded it snapped. I had my long cowstail in the other anchor and my descender wasn't yet open, so I wasn't going anywhere, but it was a good lesson, as that probably wouldn't have happened on a throughbolt, due to the projecting stub beyond the nut, and it would probably have bent. And everyone was watching me five metres above, alternately laughing or horrified, depending who it was

So I concede that placement and quality of hole (and screw) is paramount, but I'm still convinced there's nothing better for the usage I intend for them. Best I can do

 

[mikem]

Yes, in the end it all depends on the quality of the rock you're placing it in. I'm not suggesting through bolts are better, just that if you are going to use them then the hole needs to be deeper.

Presumably screws aren't ideal for placements in the roof? - where there will be more leverage on the head...

The Petzl removable ones do stress the rock in the same way as a through bolt, so probably only really have a place in rescues, or where you need a product with certification. & Possibly in highly corrosive environments (some metal mines) where you don't want to leave metal in situ.

 

[ChrisJC]

So we have put a few thousand expanding bolts in slate. They are all still there as you can't get them out again. Almost of all of them were exploration trips, so not that many remain with the anchor plate attached.

We have only had one failure, where the bolt remained attached to the rock, but a lump of rock came out of the wall. We were expecting this to occur and had rigged accordingly. I didn't fall that far.

We hit the rock with a hammer before drilling the hole, and if it sounds hollow, we find somewhere else.

We are happy with our technique.

Chris.

 

[georgenorth]

Another option to concrete screws would be M10 shield  anchors (Rawlbolts). They go in a 16mm hole, so you could re-use the hole for resin anchors if required. I probably wouldn?t fancy leaving them in-situ in a mine for longer than a few months though due to corrosion.