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Mine Exploration Forum

Author SRT - Glue-in anchor bolts assessment
Vanoord

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Joined: 28/11/2005
Location: North Wales

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SRT - Glue-in anchor bolts assessment
Posted: 23/03/2009 10:19:50
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This [web link] comes care of NWCRO and it might be of interest to people on the forum.

It's a decent assessment of the design of glue-in anchor bolts and includes some interesting stress-testing of components.

The bit that I found of most interest was a comparison between different methods of cleaning out a hole before gluing in the anchor:

Hole blown out with blower: pull-out 1060kg

Hole blown out with compressed air at 8 bar: pull-out 1560kg

Hole blown, brushed and blown with blower: pull-out 3540kg

Given the immense variability, I can't help but suspect that a mechanical bolt is preferable under many circumstances as it isn't going to be affected by how well you clear the hole out

I suppose there's also a question of whether the mechanical force of an expansion bolt might damage the rock (particularly in something like slate) - does anyone know if there are any problems with epoxy (or similar) expanding as it sets?

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Knocker

Joined: 17/06/2008

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SRT - Glue-in anchor bolts assessment
Posted: 23/03/2009 13:25:00
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No there is no expansion with chemical anchors (Well with Hilti Hit anyhow). I remember one on a site I had a carpenter fixing a balcony handrail on with bolts held by HIT. He came in complaining how crap it was and it had gone off and the handrail just pulled straight out. I went out to look at it, as soon as I looked at it, it was obvious he had not cleaned the hole, I asked him if he had cleaned it, h just replied he didn't think it was important.

The key with HIT is simply: - Blow - Brush - Blow - Brush - Blow, it takes less than a minute
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pat

Joined: 22/11/2007

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SRT - Glue-in anchor bolts assessment
Posted: 23/03/2009 16:30:45
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Even the lowest failure figure on this bolt test gives safety factor of over 10:1 for a 1 person load but as Knocker said it only takes i minute to do it properly.
i have used the "sea water series" as seen in the link and found these bolts to be an excellent choice for anchor that may be under water for some of the day.
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SimonRL

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SRT - Glue-in anchor bolts assessment
Posted: 23/03/2009 20:52:28
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Changing the subject a little to Petzl / Fixe (etc) style of expansion bolts, does anybody know any comparative tests for cleaned/thoroughly cleaned drill holes for these? Does it make as much of a difference? IP: 83.148.135.213
Vanoord

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SRT - Glue-in anchor bolts assessment
Posted: 23/03/2009 20:58:51
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As the fixing method is mechanical, I doubt it would make a massive difference?

The problem with resin would be that the resin will bond to the dust and not to the sides of the hole and thus the plug would not be connected to its surroundings, thus allowing it to pull out.

With a 'mechanical' fixing, as the bolt has force applied to it, the sleeve expands and the fixing effectively gets tighter, thus whether or not the hole has been cleaned is not particularly vital.

What I might be concerned about is that if a large force is applied to a 'mechanical' bolt, then is the force more likely to split the rock and promote failure? This isn't going to be an issue in something like granite, but in something laminar like slate it might be an issue?



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SimonRL

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SRT - Glue-in anchor bolts assessment
Posted: 23/03/2009 21:07:17
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It certainly makes enough of a difference for it to be mentioned in bolting guides and the like. A long flexible tube to blow through works very well, and you can get your face far enough away to avoid a cloud of dust in your eyes - not something that works with a straw as I found out on early bolting trips! IP: 83.148.135.213
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