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miklaw


Oct 31, 2010, 11:35 PM
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soft rock bolt testing
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Here in Australia, the Blue Mountains has pretty soft rock, you can hand drill an anchor in 5 minutes. Mechanical bolts have fallen out pretty quickly so we mostly use beefy glue-ins.

So I started testing on a chunk of soft rock in a local quarry and tested a range of gear.

Our local 2" carrots (tapered machine bolts had a minimum strength of 2500 lbs (4 tests),

2.5" carrots had a minimum of 3100lb (4 tests),

12 mm x 80 mm sleeve dynabolts had a min of 4300lb (2 tests),

80 mm leg 10 mm shaft Ubolts with polyester failed at 7360 in wet rock, and a minimum of 8480 in dry rock (and some stayed in at 10,800 lbs. the one epoxy ubolt of this size is also still in after this load.

10 mm x 100mm eyebolts bent and pulled at a mimimum of 5680 lb

This was an epoxy 80 mm Ubolt at 10,800lb which is still in place. The arrows show the point on each leg where the the ubolt entered the rock initially. The upper (right) leg has been pulled out about 10 mm, while the lower leg hasn't moved out of its hole yet.


(This post was edited by miklaw on Oct 31, 2010, 11:39 PM)
Attachments: pull2.jpg (36.4 KB)
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brokesomeribs


Nov 1, 2010, 10:45 PM
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Re: [miklaw] soft rock bolt testing [In reply to]
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miklaw wrote:
Here in Australia, the Blue Mountains has pretty soft rock, you can hand drill an anchor in 5 minutes. Mechanical bolts have fallen out pretty quickly so we mostly use beefy glue-ins.

So I started testing on a chunk of soft rock in a local quarry and tested a range of gear.

Our local 2" carrots (tapered machine bolts had a minimum strength of 2500 lbs (4 tests),

2.5" carrots had a minimum of 3100lb (4 tests),

12 mm x 80 mm sleeve dynabolts had a min of 4300lb (2 tests),

80 mm leg 10 mm shaft Ubolts with polyester failed at 7360 in wet rock, and a minimum of 8480 in dry rock (and some stayed in at 10,800 lbs. the one epoxy ubolt of this size is also still in after this load.

10 mm x 100mm eyebolts bent and pulled at a mimimum of 5680 lb

This was an epoxy 80 mm Ubolt at 10,800lb which is still in place. The arrows show the point on each leg where the the ubolt entered the rock initially. The upper (right) leg has been pulled out about 10 mm, while the lower leg hasn't moved out of its hole yet.

Interesting info. Looks like you should be using the 12mm x 80mm dynabolts from here on out. 4000 lbs is a good minimum to aim for when installing bolts.

Was all the listed hardware installed specifically for this testing or was it all old gear?


miklaw


Nov 1, 2010, 10:52 PM
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Re: [brokesomeribs] soft rock bolt testing [In reply to]
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All new gear
Dynabolts loosen very quickly in soft rock if people are falling on them, so we keep them for good rock (pretty much anywhere else in Australia).


Partner philbox
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Dec 24, 2010, 12:32 AM
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Re: [miklaw] soft rock bolt testing [In reply to]
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http://www.youtube.com/watch?v=cLW8gBhmE7A

Don't want to steal Mikl's thunder but here is a vid of his latest bolt testing in very soft sandstone.


bill413


Dec 24, 2010, 6:24 AM
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Re: [philbox] soft rock bolt testing [In reply to]
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philbox wrote:
http://www.youtube.com/watch?v=cLW8gBhmE7A

Don't want to steal Mikl's thunder but here is a vid of his latest bolt testing in very soft sandstone.

Interesting, it seems though that in each of the failures, the tripod legs were involved in the fractures.


miklaw


Dec 26, 2010, 12:30 PM
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Re: [bill413] soft rock bolt testing [In reply to]
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Agreed, but I think it's a minor effect. In harder rock the failure cone is much smaller and sits well inside the tripod legs. We also tested 2 bolts in similar very soft rock outwards with no tripod by pulling on trad gear from above, and they had similar failure strengths and very slightly bigger cones.

As explained in the soft rock bolting guide you get a mixed failure mode, with a short cone (as much as the rock can take) with the rest of the shaft showing glue bond failure.If the cone length is reduced by the tripod, the glue bond length gets a bit bigger with only a small change in failure strength.

http://routes.sydneyrockies.org.au/display/thelab/Home


phang_nga


Dec 30, 2010, 4:33 PM
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Re: [philbox] soft rock bolt testing [In reply to]
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philbox wrote:
http://www.youtube.com/watch?v=cLW8gBhmE7A

Don't want to steal Mikl's thunder but here is a vid of his latest bolt testing in very soft sandstone.

Is there not also a difference in the amount of force the bolt can take if it's not pulled in a direct outward direction? I'm guessing that this test isn't exactly realistic in light of this. Plus, check out the math at http://forum.onlineconversion.com/showthread.php?t=844 It seems for there to be a problem, the climber must fall from a fairly high height.

There are a couple of recent comments on the YouTube video that make a bit of sense.


Partner philbox
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Dec 30, 2010, 11:59 PM
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Re: [phang_nga] soft rock bolt testing [In reply to]
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Of course there is a difference between outward pull and shear. In shear these bolts would hold much more than a straight outwards pull. These tests however are demonstrating strengths of bolts in almost the absolute worst case scenarios. It should actually give quite a deal of comfort to climbers when they realise just how strong bolts are when the bolts are installed correctly in hard rock.

This rock is absolute pox.


phang_nga


Dec 31, 2010, 1:54 AM
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Re: [philbox] soft rock bolt testing [In reply to]
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philbox wrote:
In shear these bolts would hold much more than a straight outwards pull... It should actually give quite a deal of comfort to climbers when they realise just how strong bolts are when the bolts are installed correctly in hard rock.

This rock is absolute pox.

Yep, therefore perhaps it isn't as bad as the video makes it out to be. I don't think I'd climb on it.

Yep, that's part of what I got out of it... a good bolt is pretty darn bomber.

It seems like one might be safer bolting into a sheet-rock wall in a house than climbing on that rock! Crazy

I wonder if the bolts were a LOT longer if it would help? It seems like there is a flaky outer crust to this particular rock.


miklaw


Jan 2, 2011, 12:09 PM
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Re: [phang_nga] soft rock bolt testing [In reply to]
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phang_nga wrote:
Is there not also a difference in the amount of force the bolt can take if it's not pulled in a direct outward direction?
>> generally stronger

Plus, check out the math at http://forum.onlineconversion.com/showthread.php?t=844
> It's way more complicated than that, the potential energy is correct, but the force depends on the stopping time or distance, plus body movement etc


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