Drilling Directly Above Sheared Off Bolts Or Stuck Sleeves for Glue-Ins

Jim! You da man!That is a very interesting and informative pull test.

On one hand I do have concerns about a void right below a glue in, but the test shows it to be good. I am looking forward to seeing the test with a shorter glue in than void.

I think if I can get the bolt out but not the sleeve, I will just fill in the sleeve with adhesive. So then there would be no void. 

Jim Titt wrote:

... in the morning I shall do the same test with a shorter glue-in than the mechanical bolt and see.....

I am on the edge of my seat!

Taylor Krosbakken wrote:

I am on the edge of my seat!

Have to wait a bit, lot of work tomorrow then a tour in the Austrian Alps for the weekend.

Ok Jim, I guess that is acceptable. haha. I really appreciate this and I hope we can all learn a lot.

Pouring here in the Minnesota this weekend so no bolting work anyway. 

A wet weekend in Minnesota, I´m jealous!I forced myself to load up my Yamaha with camping gear and one of my sons in 70° sun and ride a couple of hours to the Austrian Alps, camp by a mountain river and eat loads of home-cured ham looking at stuff like this;-

Bolts;
I drilled 120mm deep (with a 13mm drill) and installed a 100mm bolt above it in a 12mm hole, the rock between shatters out so it´s more like a slot than two holes. This time the bolt held 42.84kN before the eye failed (higher than the first one as I used a larger diameter pin). I split the rock to see what happened. (The hole visible on the right is from another test from the side of the block).

Close-up of the failure area of the resin, you can see the crack where it breaks off and makes like a wedge supporting the bolt, there´s still 80mm of bolt which is unnaffected.

Jim Titt wrote: 
Bolts;
I drilled 120mm deep (with a 13mm drill) and installed a 100mm bolt above it in a 12mm hole, the rock between shatters out so it´s more like a slot than two holes. This time the bolt held 42.84kN before the eye failed (higher than the first one as I used a larger diameter pin). I split the rock to see what happened. (The hole visible on the right is from another test from the side of the block).
Close-up of the failure area of the resin, you can see the crack where it breaks off and makes like a wedge supporting the bolt, there´s still 80mm of bolt which is unnaffected.

Jim - great info as usual.  Even better to know this.  What glue (or glue type) are you using here?  Do you think epoxy vs a hybrid or acrylate will matter much?  (I'm typically an Epcon A7+ user)  

Jim Titt wrote: A wet weekend in Minnesota, I´m jealous!I forced myself to load up my Yamaha with camping gear and one of my sons in 70° sun and ride a couple of hours to the Austrian Alps, camp by a mountain river and eat loads of home-cured ham looking at stuff like this;-

Well now it just sounds like you are bragging ;)

Amazing information. And the cross section is really great.

Really interesting to see how as the bolt bends it just supports itself on the bottom of the lower hole it appears and then you basically have the rest of the bolt/glue/rock interface holding in more tension/pull out instead of in shear.

And thank you again so much for all of this! If you ever venture to Minnesota, let me know!

Love geeking out on these bolt threads. Impressive work Jim. Thanks. Glue-ins are strong! 

That's a vinylester, just some Swiss company I use but nothing special really.

Ed Henicle wrote: Love geeking out on these bolt threads. Impressive work Jim. Thanks. Glue-ins are strong! 

Same here, although I'm kind of more of a lurker than a contributor on these types of threads. I don't know much about glue-ins but I love learning more about them and Jim is quite a wealth of knowledge on the topic as well as being willing and able to actually conduct these types of experiments time and time again. They are only 1 data point and obviously aren't as reliable as statistically significant, organized research but are certainly a step up from the [hopefully] somewhat informed theory-craft that occurs on these forums.

Thank you Jim for being willing to sift through the BS here on MP and put up with us and all of our curiosities, questions, and thoughts. You are quite a valuable contributor to these discussions and people are able to learn a lot, or at least the ones who are willing to sift through the BS to find the little nuggets of information and knowledge. We appreciate your contributions.

One thing I'm curious about how exactly rock quality factors in to this, specifically with less-than-desirable rock quality. Around here, glue-ins are almost exclusively placed in soft rock where a glue-in will typically perform better than expansion bolts. Most of the good rock is bolted with expansion bolts because they work well enough and because most of the developers around here have limited to no experience with glue-ins as opposed to lots of experience with expansion bolts.

If I'm understanding things correctly, the void below the new glue in bolt essentially functions to change how the bolt is loaded, generally trending towards more loading in tension and less loading in sheer than would occur otherwise without the void. If I understand it correctly, rock quality a more significant factor the more the bolt is loaded in tension, playing less of role when bolts are loaded mostly in sheer.

So, in theory, the softer the rock, the more length you need in the section of the glue-in that extends beyond the void below. Is that correct?

eli poss wrote:

Same here, although I'm kind of more of a lurker than a contributor on these types of threads. I don't know much about glue-ins but I love learning more about them and Jim is quite a wealth of knowledge on the topic as well as being willing and able to actually conduct these types of experiments time and time again. They are only 1 data point and obviously aren't as reliable as statistically significant, organized research but are certainly a step up from the [hopefully] somewhat informed theory-craft that occurs on these forums.

Thank you Jim for being willing to sift through the BS here on MP and put up with us and all of our curiosities, questions, and thoughts. You are quite a valuable contributor to these discussions and people are able to learn a lot, or at least the ones who are willing to sift through the BS to find the little nuggets of information and knowledge. We appreciate your contributions.

One thing I'm curious about how exactly rock quality factors in to this, specifically with less-than-desirable rock quality. Around here, glue-ins are almost exclusively placed in soft rock where a glue-in will typically perform better than expansion bolts. Most of the good rock is bolted with expansion bolts because they work well enough and because most of the developers around here have limited to no experience with glue-ins as opposed to lots of experience with expansion bolts.

If I'm understanding things correctly, the void below the new glue in bolt essentially functions to change how the bolt is loaded, generally trending towards more loading in tension and less loading in sheer than would occur otherwise without the void. If I understand it correctly, rock quality a more significant factor the more the bolt is loaded in tension, playing less of role when bolts are loaded mostly in sheer.

So, in theory, the softer the rock, the more length you need in the section of the glue-in that extends beyond the void below. Is that correct?

Well in theory if the old mechanical bolt was long enough there´s no need to go longer with the new bolt but in reality I´d just put a longer one in just to be sure ince I wouldn´t have trusted the previous installer to have used a long enough bolt in the first place! In real soft rock I wouldn´t be putting in the 6mm rod bolt anyway, when we test them they tend to cut down into the rock below and look scary even when they hold o.k. Since drilling soft rock is easy it´s just simpler to put in a bolt made from 8mm rod or single-leg 12mm. It´s all a bit theoretical anyway since I´m talking about loads that a bolt would never experience, when I´m testing the interesting stuff starts happening in the 35 to 70kN areas, not your normal 5-6kN. You can see this if you look at the first set of photos where nothing particularly exciting happens until around 20kN and that is in an exceptionally bad case of a completely unsupported bolt.

Bolts themselves always fail in tension (well ours do), I´ve never seen one just shear off, they bend and distort the eye and either fail like the ones in the photos beside the tester pin or tear off beside the weld in the welded eye ones.

Great contribution Jim, as always!

MH