Merged topic - Spit and BP bolt removal/replacement

[TheBitterEnd]

From a conservation point of view the question is: should we install ANYTHING that we can't remove with minimal impact on the cave?

We might not expect to replace them but who knows what will happen in the future? Apart from unexpected corrosion and wear and collapses and the like meaning that bolts may need moving, there is a video on YouTube of a guy climbing up a glass fronted building using "geko" pads, if that technology develops we might not even be doing SRT in 30 years time.

 

[Bob Mehew]

'Spall' is a word used for small chips of rock. What you have seen is not spalling, it is 'cone failure' originating from the point of maximum mechanical bond about 25-30mm below  the surface.

I would define "spalling" in this way:

"Spalling is a common mechanism of rock weathering, and occurs at the surface of a rock when there are large shear stresses under the surface. This form of mechanical weathering can be caused by freezing and thawing, unloading, thermal expansion and contraction, or salt deposition." 
(From wikipedia.)

It is often used to describe the process where brickwork faces get "spalled off", or in concrete (often where carbonation has reached the reinforcing, causing corrosion expansion).

There are two different processes described there. The first process is more commonly called exfoliation. Exfoliation might occur when a resin anchor is pulled out but what Bob has seen is not exfoliation. Exfoliation is one mechanism that could produce what might be called spall but there are an infinite number of ways. Chiseling might also produce spall; it might produce it at the point of the chisel where small fragments of rock break off and it might produce it at the head of the chisel where small fragments of steel break off. You could use the term spalling for what Bob has seen but in my opinion it is bad use of the word and cone failure is a more accurate term. I'm sorry if this sounds pedantic but it is important to understand the process of what is happening not what the product is; the product might be called spall but the process is definitely cone failure.

I disagree with describing it as cone failure.  I would define cone failure as reaching down to the full depth of the anchor such that the anchor is then free.  Neither case let go to that extent in that the anchors still required considerable force to fully extract.  If you wish to define spalling as limited to small chips with no influence on the strength of the anchor, then what word do you wish to use for larger sized loss?  Exfoliation sounds good to me.

Whilst the depth corresponds to your postulate that a significant feature of the BP anchor is the shift from a straight shaft to twist, the anchor was still holding post start of 'spalling'.  Typically I failed to record pertinent data on the video around the key episodes such as strength so am unable to say if the force peaked after the 'spalling' started.  What is clear is that the anchor had hardly started to travel out of the hole and took a fair force to extract it all the way.

Do we need to agree a dictionary before starting a discussion?

 

[Simon Wilson]

Am  I being thick here? I cannot understand why anyone would want to pull a perfectly good anchor out of it's placement, except for strength tests, etc. Surely any anchor being removed will already be loose and that would be the only reason for it to be replaced. So it's going to be loads easier to pull out anyway surely? Or am I missing something?  :-\

You're not missing anything. We wouldn't want to pull out a perfectly good anchor. We might want to pull out anchor if there was doubt about it's integrity for a number of reasons. Thebitterend has it right, we don't know what might happen in the future. It's about sustainability and the principal is not doing things which can't be undone. We can't go into caves with no environmental impact but we can do things to minimise it by making sure that anchors can be removed and the hole reused and that the hole is as small as possible.

Some people have not appreciated the amount of development work that has gone into the design of my anchor and that sustainability was one part of the design criteria from the start. It is very important that the load is applied at the bottom of the hole. The shank of my anchor is tapered to avoid loading the rock nearer to the surface. No other anchor design does what my design does.

 

[Simon Wilson]

'Spall' is a word used for small chips of rock. What you have seen is not spalling, it is 'cone failure' originating from the point of maximum mechanical bond about 25-30mm below  the surface.

I would define "spalling" in this way:

"Spalling is a common mechanism of rock weathering, and occurs at the surface of a rock when there are large shear stresses under the surface. This form of mechanical weathering can be caused by freezing and thawing, unloading, thermal expansion and contraction, or salt deposition." 
(From wikipedia.)

It is often used to describe the process where brickwork faces get "spalled off", or in concrete (often where carbonation has reached the reinforcing, causing corrosion expansion).

There are two different processes described there. The first process is more commonly called exfoliation. Exfoliation might occur when a resin anchor is pulled out but what Bob has seen is not exfoliation. Exfoliation is one mechanism that could produce what might be called spall but there are an infinite number of ways. Chiseling might also produce spall; it might produce it at the point of the chisel where small fragments of rock break off and it might produce it at the head of the chisel where small fragments of steel break off. You could use the term spalling for what Bob has seen but in my opinion it is bad use of the word and cone failure is a more accurate term. I'm sorry if this sounds pedantic but it is important to understand the process of what is happening not what the product is; the product might be called spall but the process is definitely cone failure.

I disagree with describing it as cone failure.  I would define cone failure as reaching down to the full depth of the anchor such that the anchor is then free.  Neither case let go to that extent in that the anchors still required considerable force to fully extract.  If you wish to define spalling as limited to small chips with no influence on the strength of the anchor, then what word do you wish to use for larger sized loss?  Exfoliation sounds good to me.

Whilst the depth corresponds to your postulate that a significant feature of the BP anchor is the shift from a straight shaft to twist, the anchor was still holding post start of 'spalling'.  Typically I failed to record pertinent data on the video around the key episodes such as strength so am unable to say if the force peaked after the 'spalling' started.  What is clear is that the anchor had hardly started to travel out of the hole and took a fair force to extract it all the way.

Do we need to agree a dictionary before starting a discussion?

With the BP anchor fragmentation, spalling, disintegration. smashing or breakage of the rock occurs emanating from the point of maximum mechanical bond at the start of loading and that point is where the twists start. The fact that it still has considerable mechanical bond after the initial cone failure does not matter because the cone failure has already rendered the hole unable to be reused.

Cone failure can occur at any point down the hole. With a through-bolt if cone failure occurs it will occur at the point of maximum mechanical bond which is where the taper is and a short distance from the bottom of the hole. It will leave  the bottom part of the hole intact. The difference between that cone failure and the BP cone failure is the proportion of the hole that is left intact.

'Exfoliation' has a specific meaning in geomorphology and refers to breaking off of sheets - from the Latin folio. Exfoliation occurs to limestone and other rocks when the surface has altered by exposure to the elements. With limestone the exfoliation typically is about 2-3mm deep. In American geomorphological journals 'spalling' is sometimes used instead of 'exfoliation'. Spalling is also used in engineering to describe the breaking off of fragments of any material and does not have a very specific definition.

Can we stop getting hung up on words. The main point is that you can't get a BP anchor out without breaking the rock.

 

[martinm]

You're not missing anything. We wouldn't want to pull out a perfectly good anchor. We might want to pull out anchor if there was doubt about it's integrity for a number of reasons. Thebitterend has it right, we don't know what might happen in the future. It's about sustainability and the principal is not doing things which can't be undone. We can't go into caves with no environmental impact but we can do things to minimise it by making sure that anchors can be removed and the hole reused and that the hole is as small as possible.

Some people have not appreciated the amount of development work that has gone into the design of my anchor and that sustainability was one part of the design criteria from the start. It is very important that the load is applied at the bottom of the hole. The shank of my anchor is tapered to avoid loading the rock nearer to the surface. No other anchor design does what my design does.

Thanx Simon. That makes perfect sense, Hole as small as possible. Load applied at the bottom of the hole. I don't like the idea of having to drill 16 or 18mm holes. A 12mm would be much better and would take less power to drill. The tapered design seems a good idea too, when a load is applied it would tend to grip more tightly in the hole as well wouldn't it! 

 

[Simon Wilson]

My design is quite sophisticated and took months of development work. I has several tapers and it would take a long time to fully explain it all. As well as not loading the rock near the surface it also has a taper-lock effect which takes place as it starts to move under load.

 

[Bob Mehew]

I am not going to try and explain why I think your view on words is wrong, save to comment that both of us felt one 'spalled' hole was potentially OK to reuse after drilling the hole a bit deeper.  In part you need to see the photos.

The main point is that you can't get a BP anchor out without breaking the rock.

Not true!  We got 2 out of 4 out without breaking the rock.  We were deliberately not placing our load directly around the hole which you ingenious device does and which may well stop rock breaking.  We also have a possible route of lifting the head by a lever, cutting the head off and then core drilling the rest out.

Also if I recall correctly, you have only tested your anchors in one area of limestone which was not a quarry nor on a fault.  So it might be solely a rock related problem rather than a design of anchor problem. 

 

[bograt]

We also have a possible route of lifting the head by a lever, cutting the head off and then core drilling the rest out.

I imagine you are thinking about core drilling round the old anchor to get it out, then inserting a fresh resin anchor into the hole thus produced?
Have you any thoughts on removing the old resin left behind in the hole? although the bond between this and the rock might be adequate, how about the bond between the new resin and the old stuff left with a smooth surface by core drilling?

 

[Simon Wilson]

Also if I recall correctly, you have only tested your anchors in one area of limestone which was not a quarry nor on a fault.  So it might be solely a rock related problem rather than a design of anchor problem.

You've forgotten that I've tested my anchor in weathered gritstone, that the field I've done most of my testing in has been quarried in parts and that my anchor was tested in several planes in quarried faces and boulders all with the Rawl resin. When I changed to Fischer I also purposely changed the method and did all the tests in one bed so I could eliminate as much as possible the effects of variation in the physical properties of the rock. Perhaps I need to explain that in the test report on my website. I have plans to test at other sites.

 

[Bob Mehew]

Have you any thoughts on removing the old resin left behind in the hole? although the bond between this and the rock might be adequate, how about the bond between the new resin and the old stuff left with a smooth surface by core drilling?

The theory is that you go back in afterwards with a rotary percussion drill to roughen up the sides of the hole.

PS Sorry, getting out the report on last Sunday's work is taking me longer than expected.

 

[Simon Wilson]

Core drilling around a BP anchor would leave a hole of at least 22mm diameter and probably bigger.

 

[Badlad]

Hand held coring is not likely to leave a very smooth hole.  My experience of coring out for pipes and conduits through walls is that you wobble around leaving circular grooves in the hole.  What is likely to be more of a problem is following the same line as the original hole even if you're using the same diameter bit.  A larger diameter bit will probably make it even harder.  The shape and style of the hole, any remaining resin, it's surface area and shape will introduce variables which are going to be difficult to allow for in any testing.  In practice coring may be be a problematic option.

 

[Simon Wilson]

You would core drill part way then still need a puller. All done hanging on a rope. Not very practical.

 

[bograt]

You would core drill part way then still need a puller. All done hanging on a rope. Not very practical.

I suspect the principle of core drilling is based upon removal of the loop head before drilling, how are you going to attach the puller?

 

[Simon Wilson]

You would core drill part way then still need a puller. All done hanging on a rope. Not very practical.

I suspect the principle of core drilling is based upon removal of the loop head before drilling, how are you going to attach the puller?

Errrrr,, oh yes! So you would have to core drill 100mm deep hanging on a rope whilst squirting water from a squeezy bottle.

 

[SamT]

FYI

The BMC did a lot of testing of resin bolts over the last few years. They plumped for the BP bolt in the end. 

https://www.thebmc.co.uk/bmc-better-bolts-campaign

However, my point is that they tried (and I mean went out, bought the kit and tried it) core drilling around an old spit. They found that it was just too technically and practically difficult to warrant any further experimentation. 
Remember a spit is only 12mm in diameter and only about 20mm deep.  If this was just too much of a pain in the ass to consider. Coredrilling something in the region of 18mm diameter and 150mm deep, whilst dangling.  Forget it.
There is also the issue that the 'back' of the hole will still be attached.  At least with a spit, you can possibly still screw a hanger to it to pull it.  If you chopped the eye off, then how, after core drilling, are you going to extract the 'plug' if its still attached at the back.
I just don't think its even worth the effort of typing any more on the topic of core drilling, its a bit of a non starter.

 

[andrew]

People dismiss things too easily

I successfully replaced a hand placed spit today, after trying it on Saturday. Just got the photos and stuff back after leaving them behind, but will deal with that tomorrow.

It takes less than 5 mins, the only hard part is getting the spit out of the core after, more tedious than hard. It leaves a 16mm hole, that I roughened up with a drill.

You will need one of these, well probably more than one, but so far I  have only done 2 spits, so that is a matter of more testing

http://www.ebay.co.uk/itm/271381875583
Select the 16mm one
Guess this link will break in time, so it is a 16mm diamond core bit (does not say a make or anything, and came in a white box, but of ?7.16 it seems great)

Quaking anyone?

Tend to agree that bigger will be more of a pain, and do not think that it is a practical one for a BP anchor, especially if there is an alternative that does come out.

 

[Simon Wilson]

Thanks Andrew. That is what I expected. It is practical to core drill round a Spit but not easy.

My puller will pull out most resin anchors but not a BP.

 

[Antwan]

My puller will pull out most resin anchors but not a BP.

Good news for people hanging on them at least.

 

[TheBitterEnd]

There is also the issue that the 'back' of the hole will still be attached.  At least with a spit, you can possibly still screw a hanger to it to pull it.  If you chopped the eye off, then how, after core drilling, are you going to extract the 'plug' if its still attached at the back.

I've done this with big cores in reinforced concrete, you just hammer a small chisel down the side and break the core up. If you are lucky it comes out in one.