Merged topic - Spit and BP bolt removal/replacement

[Mark Wright]

Thanks for clarifying that Sam and thanks for putting the effort in. I couldn't do it as the flack would wind me up too much.

I was envisaging wiggling the drill around as the hole was drilled, making it oval shaped. I bet its hard not to get a bit of a wobble going in some of the more awkward locations with such a big and heavy drill though.

I have similar concerns to Bob regarding damaging the rock surface when they are eventually removed. Technically, the ones that are already in should be in the best location available, if they have to be replaced in a different location that is not ideal from a conservation point of view and not ideal for the future generations of cavers.

I'd rather not get drawn into the politics but, a bolt that can be installed with a lightweight drilling machine with a 12mm bit and drills considerably more than 3 holes per battery and doesn't damage the rock when it is removed sound perfect. 

Mark

 

[Bob Mehew]

Like Mark, I wish to avoid dropping into the politics of anchor installation.  But I will comment that:

a) Installation procedures are specified by regional caving councils rather than the BCA E&T Committee.
b) Some resin anchor suppliers do say to not use diamond drills with their product.
c) A reasonably irregular hole will allow for the resin to form a mechanical interlock with the rock if the resin / rock bond should break. 
d) The extent of irregularity has not been defined in numerical terms.  But the irregularities need to be not only across the diameter of the hole but also down the depth of the hole to stop both rotation and / or extraction. 
e) I think there has been a handful or two of anchors placed under the NCA / BCA scheme which have failed at the resin / rock bond out of some 5000 placed anchors.  The irregular hole shape / mechanical interlock has meant that the anchor has resisted extraction under normal forces seen in caving.  (Indeed the reported efforts to remove such anchors suggest the force is a substantial fraction of the peak force for a 'perfect' anchor.)
f) This is one of the 'back up' features of this resin anchor system which give it such reliability.
g) There are many reports that the BP twisted anchor does not easily fit within the suppliers specified 16mm hole.  Indeed one region recommends that installers carry with them a especially 'shaved down' BP anchor (where the twisted part of the anchor has been ground down to remove a fraction of a mm of metal) to use when checking depth of hole and orientation of the anchor head. 

I am grateful to those installers who have freely spoken to me of their experiences within the anchor placement program which enables me to make the above comments.

 

[Simon Wilson]

The IC resin anchor website has been updated with the reports of tests on anchors placed in previously used 12mm holes and on anchors placed in 18mm holes and previously used 18mm holes.

Obviously a hole can only be reused if the previous anchor can be removed without too much damage to the rock.

http://www.resinanchor.co.uk/3.html

 

[Bob Mehew]

Andrew Atkinson and myself carried out 4 extractions of Bolt Product anchors on Sunday.  The anchors were place in two boulders, with the aim of one anchor being roughly at right angles to the bedding plane and the other anchor parallel to the bedding plane.  All anchors were extracted using the BCA anchor puller with over 40kN force in the axial mode.  For one boulder, we drilled out a fairly small amount of resin around the heads prior to extracting the anchors.  They both came out with only one small trivial amount of spalling.  In contrast, the other bolder showed massive spalling, covering roughly 50cm by 40cm and 30cm by 30cm of the surface around the hole.  (We had decided to not drill out surplus resin for these two anchors, but consider that this made no difference to the extensive spalling witnessed.) 

The results leave us sufficiently concerned with the use of these anchors to recommend that further work be done to see if an alternative extraction method can avoid spalling.  We note Bolt Products recommend cutting the head off, and then core drilling the rest of the anchor out.  Because we currently recess our anchors it appears to us that it will be difficult to cleanly cut the head off, so we are unsure that their method will work for us.

We will write the work up with photographs and videos in due course.

 

[TheBitterEnd]

Just out of interest and I'm sure it will be in your write-up but was the spalling parallel or normal to the bedding and to what depth (roughly) did the spalling extend?

 

[Simon Wilson]

Easy peasy resin anchor removal.

http://www.resinanchor.co.uk/5.html

 

[SamT]

does the circular contact point around the circumference prevent the spalling??

Has it been tested on BP bolts yet??

Did you drill out any resin first ??

 

[TheBitterEnd]

Yes, nice one Simon 

 

[Simon Wilson]

does the circular contact point around the circumference prevent the spalling??

Has it been tested on BP bolts yet??

Did you drill out any resin first ??

No drilling, no heating just pulling.

I don't own any BP anchors but if somebody left some anchors lying around for no apparent reason without any labels do you think I would be justified in pulling them out in order to test my puller in the interest of all cavers?

 

[TheBitterEnd]

I don't think so without asking whoever placed them, they could be part of some other program. Why not just get together with Bob Mehew and do some tests?

 

[Simon Wilson]

I don't think so without asking whoever placed them, they could be part of some other program. Why not just get together with Bob Mehew and do some tests?

So you don't think I would be doing a public service by removing some of the many anchors which detract from an oft-frequented public open space near Ingleton. If the people that installed them didn't want them touching I think they would have labelled them.

The answer to your question is that I probably will do sometime but we don't know when.

 

[andrew]

Probably only just fits over a BP anchor, measuring by eye it is 48mm but I am sure that would squash. The dmm are slightly bigger, but I am sure with a different tube it could be used.

What is the max force? Over 60KN can be needed for BP.

It would be good to test it on the different anchors in play

 

[Bob Mehew]

I think

http://www.resinanchor.co.uk/5.html

is one of a number of Singing River anchors put in a large slab by us some years ago on the middle bench of the quarry.  Please do not touch all the anchors on the lower bench; some are used by local OECs for wheel chair users.  ( But I don't know which.)

Was the thread HT?  And can I borrow it for 6 & 7 Dec if you are not free?

Just out of interest and I'm sure it will be in your write-up but was the spalling parallel or normal to the bedding and to what depth (roughly) did the spalling extend?

Both!  Several cm.  One possible explanation is blast damage since they were both 'quarry' boulders.  And as has been pointed out to me, a fault is likely to put a fair amount of damage into the local rock. 

 

[TheBitterEnd]

Both!  Several cm.  One possible explanation is blast damage since they were both 'quarry' boulders.  And as has been pointed out to me, a fault is likely to put a fair amount of damage into the local rock.

Thanks

 

[Simon Wilson]

I think

http://www.resinanchor.co.uk/5.html

is one of a number of Singing River anchors put in a large slab by us some years ago on the middle bench of the quarry.  Please do not touch all the anchors on the lower bench; some are used by local OECs for wheel chair users.  ( But I don't know which.)

It was a Singing Rock anchor on the sloping slab. There are several anchors on that slab in various states, some bent over, partly pulled out or partly broken off but all obviously of no use.

 

[Simon Wilson]

Andrew Atkinson and myself carried out 4 extractions of Bolt Product anchors on Sunday...............  In contrast, the other bolder showed massive spalling, covering roughly 50cm by 40cm and 30cm by 30cm of the surface around the hole.  (We had decided to not drill out surplus resin for these two anchors, but consider that this made no difference to the extensive spalling witnessed.) 

'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.

 

[cavermark]

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).

 

[Simon Wilson]

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.

 

[martinm]

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?  :-\

 

[Bottlebank]

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?  :-\

They don't last for ever, sooner or later many will need replacing.