Resin anchor countersinking (split from Blacknor Hole bolts)

[Simon Wilson]

Unfortunately they were install incorrectly with the bolt head being proud of the surface rather than the welded part set down into a groove.

I guess since neither U-staples (are people really still making and using them?) nor the BP anchors now generally being installed (at least by the bolt fund) need to be recessed (the twisted leg makes this unnecessary, according to the manufacturer) Portland climbers would never normally need to recess an anchor head.

I don't think any manufacturers of resin anchors recommend countersinking them. It was a measure introduced by cavers to reduce the movement of loose anchors. I can't see why a twisted leg would make any difference to the movement of a loose anchor.

[andrewmc]

I don't think any manufacturers of resin anchors recommend countersinking them. It was a measure introduced by cavers to reduce the movement of loose anchors. I can't see why a twisted leg would make any difference to the movement of a loose anchor.

I assumed that the countersinking was to increase the resistance against rotation to prevent anchors becoming loose (i.e. breaking the relatively weak adhesive glue-anchor bond) in the first place, rather than reducing the wobble of anchors that have already, to some degree, 'failed'.

Something like the Fixe or Petzl resin anchors have little or no mechanical keying against rotation. Presumably the point of countersinking is that the sticky-out-ness of the head provides something to resist rotation. The BP anchors (and probably yours as well as they don't have a round cross-section, although possibly less so) have significantly more sticky-out-ness to resist rotation than an otherwise round anchor.

Note my use of the technical term sticky-out-ness.

[Simon Wilson]

I don't think any manufacturers of resin anchors recommend countersinking them. It was a measure introduced by cavers to reduce the movement of loose anchors. I can't see why a twisted leg would make any difference to the movement of a loose anchor.

I assumed that the countersinking was to increase the resistance against rotation to prevent anchors becoming loose (i.e. breaking the relatively weak adhesive glue-anchor bond) in the first place, rather than reducing the wobble of anchors that have already, to some degree, 'failed'.

Something like the Fixe or Petzl resin anchors have little or no mechanical keying against rotation. Presumably the point of countersinking is that the sticky-out-ness of the head provides something to resist rotation. The BP anchors (and probably yours as well as they don't have a round cross-section, although possibly less so) have significantly more sticky-out-ness to resist rotation than an otherwise round anchor.

Note my use of the technical term sticky-out-ness.

I can't see why the shape of the cross section of the metal part of the anchor has any bearing on rotation of a loose anchor. With every anchor I've seen that has significant movement the whole resin plug is moving. The main reason why anchors become loose appears to be resin shrinkage.

By the way - I forgot to say that the IC anchor is intended to be counteresunk but that's mainly because it has a round opening.

[andrewmc]

I can't see why the shape of the cross section of the metal part of the anchor has any bearing on rotation of a loose anchor. With every anchor I've seen that has significant movement the whole resin plug is moving. The main reason why anchors become loose appears to be resin shrinkage.

Fair enough - although presumably less than fastidious cleaning of the hole with suitable brushes and blowers would also give a weak bond between resin and rock.

[Bob Mehew]

I can't see why the shape of the cross section of the metal part of the anchor has any bearing on rotation of a loose anchor. With every anchor I've seen that has significant movement the whole resin plug is moving. The main reason why anchors become loose appears to be resin shrinkage.

Fair enough - although presumably less than fastidious cleaning of the hole with suitable brushes and blowers would also give a weak bond between resin and rock.

There was one embarrassed installer who used a washing up liquid bottle to jet water into the hole to clean them.  It was belatedly realised the loose anchors he had installed (no resin to rock chemical bond) was due to the bottle not having been thoroughly cleaned out. 

I should add that one of the checks on the resin has been to show it will work under wet conditions. 

In theory resin shrinkage occurs both ways, but presumably the 'irregularities' of the rock are far less than the designed 'irregularities' of most anchor types.  One of the positive features of the resin anchor is that even with the chemical bonding gone, the mechanical interference between resin and rock due to those irregularities still takes a lot of effort to overcome.  But no doubt the resin will wear with usage  once the chemcial bond has gone.

Have you published your shrinkage work Simon? 

[Simon Wilson]

I can't see why the shape of the cross section of the metal part of the anchor has any bearing on rotation of a loose anchor. With every anchor I've seen that has significant movement the whole resin plug is moving. The main reason why anchors become loose appears to be resin shrinkage.

Fair enough - although presumably less than fastidious cleaning of the hole with suitable brushes and blowers would also give a weak bond between resin and rock.

There was one embarrassed installer who used a washing up liquid bottle to jet water into the hole to clean them.  It was belatedly realised the loose anchors he had installed (no resin to rock chemical bond) was due to the bottle not having been thoroughly cleaned out. 

I should add that one of the checks on the resin has been to show it will work under wet conditions. 

In theory resin shrinkage occurs both ways, but presumably the 'irregularities' of the rock are far less than the designed 'irregularities' of most anchor types.  One of the positive features of the resin anchor is that even with the chemical bonding gone, the mechanical interference between resin and rock due to those irregularities still takes a lot of effort to overcome.  But no doubt the resin will wear with usage  once the chemcial bond has gone.

Have you published your shrinkage work Simon?

Chemical bonding? Can you give evidence for that?

A "lot of effort to overcome"? How much is a lot? How many times has this 'lot of effort' been seen?

[Bob Mehew]

Chemical bonding? Can you give evidence for that?

A "lot of effort to overcome"? How much is a lot? How many times has this 'lot of effort' been seen?

After one has extracted a resin bonded anchor, some resin can remain stuck to the metal.  It chips off.  I think 'chemical bond' is a reasonable description of that phenomena.

When you pull a resin bonded anchor embedded in rock, the applied force rises to a high level.  There is distortion of the 'P' head by around 6kN.  Continuing to increase the force, there is a sudden loud crack and the force falls back some kN.  The anchor may move somewhat but remain 'lodged in the rock'.  It then requires more effort to complete the extraction as the anchor comes out of the hole.  I have a set of videos from work on testing BP anchors which show a peak forces above 20kN and subsequent forces above 10kN.  I have witnessed similar behaviour with other BP anchors. 

I have been given a similar description for extracting Eco anchors.  I also hold a set of data produced by the late Stu Goodwill with his test rig (regrettably lost following his tragic death) on Eco anchors, one example of which is attached (I hope).  Similar behaviour is shown in his work in pulling at 45 degrees off the axial axis and in shear.

I recall witnessing some of your work on IC anchors showing a similar behaviour but accept it is probably far less pronounced. 

I should add that the P head distortion at low forces is why BCA decided to go against testing anchors.  I know that DCA claim they can avoid distortion but I suspect only by testing decidedly 'off axis'.

[Simon Wilson]

You have shown evidence that there is a bond. You have not shown any evidence that there is a chemical bond. If you maintain that there is a chemical bond can you explain how it occurs? What is the chemical interaction between the stainless steel and the resin?

[droid]

Are you talking ionic or covalent bonds, Simon?

[Simon Wilson]

Are you talking ionic or covalent bonds, Simon?

That's part of the question I'm asking Bob.

[Bob Mehew]

You have shown evidence that there is a bond. You have not shown any evidence that there is a chemical bond. If you maintain that there is a chemical bond can you explain how it occurs? What is the chemical interaction between the stainless steel and the resin?

Ah, apologies for misleading you; I was thinking of a form of chemical bonding known as Van der Walls bonding rather than covalent or ionic bonding.  My use of the adjectives chemical and mechanical was an attempt to clearly differentiate between two types of bonding present in this system rather than to imply that there had been a major chemical reaction between resin and metal surface as you appear to have understood.

Can you suggest better descriptors for these two mechanisms which help an resin bonded anchor to resist the extraction force?

[Simon Wilson]

You have shown evidence that there is a bond. You have not shown any evidence that there is a chemical bond. If you maintain that there is a chemical bond can you explain how it occurs? What is the chemical interaction between the stainless steel and the resin?

Ah, apologies for misleading you; I was thinking of a form of chemical bonding known as Van der Walls bonding rather than covalent or ionic bonding.  My use of the adjectives chemical and mechanical was an attempt to clearly differentiate between two types of bonding present in this system rather than to imply that there had been a major chemical reaction between resin and metal surface as you appear to have understood.

Can you suggest better descriptors for these two mechanisms which help an resin bonded anchor to resist the extraction force?

There are two types of bond in action in a newly installed anchor and neither of them is a chemical bond.

I think the type of bond you are talking about is more commonly called dispersive adhesion. From what I've read it can get very complicated. I'm not going to pretend to have much knowledge of this type of adhesion. I researched it at the very earliest stages of the development of the IC anchor and learned enough for me to decide it was irrelevant because it is relatively weak and is quickly destroyed as the resin shrinks.

Every DMM anchor I've pulled out from a wet cave has peat staining on the shanks showing that water has got between the metal and the resin.

After researching the types of bond between the resin and the metal I decided that I only needed to consider mechanical bond and proceded to design an anchor that maximised the use of mechanical bond. After testing six prototypes the final design performs well and loads the rock consistently at the bottom of the hole by mechanical means. No other resin anchor design for caving or climbing is designed to load the rock at the bottom of the hole. The realisation that only mechanical bond matters was important in the success of the design.

[Bob Mehew]

I accept the IC anchor is more focused on mechanical bonding.  But as you admit, the IC anchor does not reflect the behaviour of Eco and BP anchors which I suggest has two distinct forms of bonding. 

More significantly, this debate started from a question about the effort required to extract an anchor.  Do you accept that even when the form of bonding which stops movement of the anchor has failed, (such as you showed in your video at https://ukcaving.com/board/index.php?topic=24698.msg306398#msg306398) that the Eco & BP anchors still requires a substantial force to extract? 

I suggest that it does and that fact is a useful safety feature which avoids an otherwise catastrophic failure mode.  I emphasise that I am not suggesting that a slightly moving anchor does not need to be replaced at some time.  But that the evidence for Eco and BP anchors does mean that a slightly moving anchor does not need to be immediately taken out of use.

[Simon Wilson]

More significantly, this debate started from a question about the effort required to extract an anchor.  Do you accept that even when the form of bonding which stops movement of the anchor has failed, ...

That would be the same bond that holds the anchor in the hole. 

... that the Eco & BP anchors still requires a substantial force to extract? 

No.

I emphasise that I am not suggesting that a slightly moving anchor does not need to be replaced at some time.  But that the evidence for Eco and BP anchors does mean that a slightly moving anchor does not need to be immediately taken out of use.

But you're only guessing. Personally, if I'm going to hang my life off a 25 year old anchor I'd like more than one person's insufficiently informed guess about it's reliabilty.

[Bob Mehew]

I emphasise that I am not suggesting that a slightly moving anchor does not need to be replaced at some time.  But that the evidence for Eco and BP anchors does mean that a slightly moving anchor does not need to be immediately taken out of use.

But you're only guessing. Personally, if I'm going to hang my life off a 25 year old anchor I'd like more than one person's insufficiently informed guess about it's reliabilty.

You dismiss the material I put forward.  So I take it you subscribe to the catastrophic failure mode.  In which case why have you not organised a change to the CNCC web site information on anchors at https://cncc.org.uk/fixed-aids/safety.php given you are the CNCC Anchor Co-ordinator?  It still states "Slight flexing or rotational movement (+/-1mm) of the anchor, as long as there is no egress of the anchor or resin from the hole, is acceptable but any more and the anchor should not be used."  I recall we debated this topic at E&T several years ago when you took the zero movement line. 

It does not worry me if you do switch to something like "Don't use any anchor if it moves", since that is being even more prudent than me and some others on E&T felt was necessary.  But please be aware that not making the change does place upon you with your CNCC function a personal liability if something does go wrong.