Minimum Bolt Spacing Standards (when patching an old hole and redrilling a new one)

What are peoples' thoughts?  I've heard one somewhat knowledgeable person say 2.5x the embedment depth of the new bolt.  I also vaguely remember someone saying in this forum that they'll  drill a new hole just above the old bolt/hole and place the new glue-in so that it covers the old hole and at a depth well beyond that of the old one.  (I tried to find the thread, but didn't quickly or easily and gave up)  In the latest highlining video about Shawn chopping highline bolts in Yosemite, he references a similar technique.  If a hole is filled with adhesive (epoxy or vinylester) and stainless steel, is it okay to treat it as a non-hole?  

Yes, just place the new bolt on the old one.

Is there some study or technical manual indicating that this is a good idea?  It's a bit of a departure from the historical norm of a minimum of 2.5x the depth of the hole and selling that concept to others by saying 'I read about it on Mountain Project' doesn't seem viable.

Also, is it a universally applicable method or does it vary by rock type, type of old bolt in the old hole, depth of the old hole, etc. etc.  I'm interested in adopting this technique if it is indeed viable, but want to learn a lot more about it before applying it and am unsure of where to do so.

Hmm, personally I think "I read about it on Mountain Project" is a viable justification when Jim wrote it. 

Here is the forum I think you were looking for. 

https://www.mountainproject.com/forum/topic/116970396/drilling-directly-above-sheared-off-bolts-or-stuck-sleeves-for-glue-ins#ForumMessage-116974304

I have a feeling if you are on YouTube later this morning you might find further testing on this concept. 

Max Tepfer wrote:

What are peoples' thoughts?  I've heard one somewhat knowledgeable person say 2.5x the embedment depth of the new bolt.  I also vaguely remember someone saying in this forum that they'll  drill a new hole just above the old bolt/hole and place the new glue-in so that it covers the old hole and at a depth well beyond that of the old one.  (I tried to find the thread, but didn't quickly or easily and gave up)  In the latest highlining video about Shawn chopping highline bolts in Yosemite, he references a similar technique.  If a hole is filled with adhesive (epoxy or vinylester) and stainless steel, is it okay to treat it as a non-hole?  

i'm thinking that looking for a fast hard rule is not the way to go.  i generally try to reuse the old hole first, unless it's going to be too much of a pain/unfeasible to go that route.  if that's the case and you have to drill a new hole i would look at the best possible placement (obviously opinions on that will very, but i try to use my best judgement) and then take it from there.  

even with ss you need to think about the conditions rather than just saying 'it's ss, it's fine' - let's say for example as a hypothetical, you've got a corroding ss bolt at a seaside crag, which you're going to replace with titanium.  you can't get the bolt out and now drill right above it to put in your glue-in ti bolt.  probably not ideal (ie there are better options).  there are a lot of other factors to consider, rock quality, original/new bolt diameter/length, etc.

The issue of bolt spacing is when both bolts are loaded. On old unused hole doesn't have much effect on a nearby bolt. When drilling a new hole near an abandoned hole I would space the holes something like 5 hole diameters apart. The problem with closely spaced bolts when both are loaded is that the pullout failure cone for two bolts isn't much different than for one bolt.

https://en.wikipedia.org/wiki/Concrete_cone_failure

https://www.fastener-world.com/data/pdf_download/FW_182_E_271.pdf

Max Tepfer wrote:

Is there some study or technical manual indicating that this is a good idea?  It's a bit of a departure from the historical norm of a minimum of 2.5x the depth of the hole and selling that concept to others by saying 'I read about it on Mountain Project' doesn't seem viable.

Also, is it a universally applicable method or does it vary by rock type, type of old bolt in the old hole, depth of the old hole, etc. etc.  I'm interested in adopting this technique if it is indeed viable, but want to learn a lot more about it before applying it and am unsure of where to do so.

As Bobby Hutton has noted I wrote the information after testing. No doubt he/they are testing as well so you'll get an independent result. It's common practice in Europe as we understand why the spacing rule is applied in construction i.e it has no relevance in our scenario.

Jim Titt wrote:

As Bobby Hutton has noted I wrote the information after testing. No doubt he/they are testing as well so you'll get an independent result. It's common practice in Europe as we understand why the spacing rule is applied in construction i.e it has no relevance in our scenario.

Bobby and Ryan just put it up. Good to go.

Told you!

old5ten wrote:

i'm thinking that looking for a fast hard rule is not the way to go.  i generally try to reuse the old hole first, unless it's going to be too much of a pain/unfeasible to go that route.  if that's the case and you have to drill a new hole i would look at the best possible placement (obviously opinions on that will very, but i try to use my best judgement) and then take it from there.  

even with ss you need to think about the conditions rather than just saying 'it's ss, it's fine' - let's say for example as a hypothetical, you've got a corroding ss bolt at a seaside crag, which you're going to replace with titanium.  you can't get the bolt out and now drill right above it to put in your glue-in ti bolt.  probably not ideal (ie there are better options).  there are a lot of other factors to consider, rock quality, original/new bolt diameter/length, etc.

Yeah, totally.  More than a hard and fast rule, I'd be stoked to come away from this thread having learned the nuances of a new technique before going out and applying it without first fully understanding it. (now that I think about it, I should probably relabel this thread to better reflect that) Before going out and rebolting a route using some method I sort of read about on the internet and watched a youtube video about, I'd like to understand how all of the considerations you listed (rock quality relative bolt diameters and depths, etc.) affect how and when to use this method.  

All the testing done in that video was done in granite.  I wonder if they'll get the same numbers in softer rock?  Also, those were brand new placements.  I wonder if this method ages differently than a traditionally placed glue in?  Honestly, I don't see myself using it all that often as usually the old bolt comes out without too much hassle.  That being said, it would be super useful to have this as an option for situations that call for it, but I'm sure there's still a lot I don't know about it and I'd like to change that first.

Max Tepfer wrote:

Yeah, totally.  More than a hard and fast rule, I'd be stoked to come away from this thread having learned the nuances of a new technique before going out and applying it without first fully understanding it. (now that I think about it, I should probably relabel this thread to better reflect that) Before going out and rebolting a route using some method I sort of read about on the internet and watched a youtube video about, I'd like to understand how all of the considerations you listed (rock quality relative bolt diameters and depths, etc.) affect how and when to use this method.  

All the testing done in that video was done in granite.  I wonder if they'll get the same numbers in softer rock?  Also, those were brand new placements.  I wonder if this method ages differently than a traditionally placed glue in?  Honestly, I don't see myself using it all that often as usually the old bolt comes out without too much hassle.  That being said, it would be super useful to have this as an option for situations that call for it, but I'm sure there's still a lot I don't know about it and I'd like to change that first.

sounds like you already have a pretty good head and are asking all the right questions (and yes, life is very different with solid granite).  personally, the first thing i try to ascertain if i'm not redrilling the same hole is 'can i make this anchor better?' and take things from there.  frequently (most of the time) you are (hopefully) using a replacement bolt that is longer and/or thicker than the original and concern in terms of proximity to an original bolt (different from an original empty hole) are actually quite minimal (and rock quality/configuration are more important imho). 

mattm wrote:

Bobby and Ryan just put it up. Good to go.

hmmmmm... 6:12 - 'so the rope is not rubbing the rock' - huh???

old5ten wrote:

hmmmmm... 6:12 - 'so the rope is not rubbing the rock' - huh???

Highline context. Some highliners use a static rope to rig directly thru the bolts. 

Bobby Hutton wrote:

Highline context. Some highliners use a static rope to rig directly thru the bolts. 

ahhhh... (lightbulb turns on in small climbing brain ;-)

Max Tepfer wrote:

Yeah, totally.  More than a hard and fast rule, I'd be stoked to come away from this thread having learned the nuances of a new technique before going out and applying it without first fully understanding it. (now that I think about it, I should probably relabel this thread to better reflect that) Before going out and rebolting a route using some method I sort of read about on the internet and watched a youtube video about, I'd like to understand how all of the considerations you listed (rock quality relative bolt diameters and depths, etc.) affect how and when to use this method.  

All the testing done in that video was done in granite.  I wonder if they'll get the same numbers in softer rock?  Also, those were brand new placements.  I wonder if this method ages differently than a traditionally placed glue in?  Honestly, I don't see myself using it all that often as usually the old bolt comes out without too much hassle.  That being said, it would be super useful to have this as an option for situations that call for it, but I'm sure there's still a lot I don't know about it and I'd like to change that first.

Normally one tests in the strongest rock possible to get results regarding the bolt/glue strength and not distorted by other factors, how rock strength effects the pull-out strength is well known already. At the end of the day it's almost impossible to correctly glue in a bolt that would fail in a climbing application as no-one makes them, if the rock is a bit soft then use a longer one.

Hello Jim,

I'd disagree with that last statement. This techniques poses a risk to the strength of the rock and if actually contacting the old hole could reduce the resin-rock mechanical interlock. As such the testing should evaluate those things. The video doesn't test those at all -- by using uncracked granite they are almost assuring metal failure because granite is so strong and these anchors are long enough to have a significant failure cone. Failure load statistics from those tests are useless because they don't have anything to do with the rock/resin. The statistics are based on the metal component failure. If you want statistical insight on how this technique affects placement strength you would want to use softer rock and/or shorter bolts so that the failure mechanism is resin or rock and then compare your results.

If I put new tires on two new cars and drive into a wall without braking can I compare the grip of the tires? Nope, because my test is not evaluating that despite the cars having different tires. Maybe the airbags though... 

As an engineering study this fails, hard. That is not necessarily saying that the test is unsafe -- that is saying their testing doesn't evaluate what they want it too -- also the huge variety of resins used and rock properties mean that taking a test like this, even if it had ben well done, would potentially be dangerous if using another resin or in different rock. Most climbing anchors are designed to be very robust and have more strength than needed. A lot of rock we see out there is very strong. Each instance still takes thoughtful consideration; and, in general, a placement should be stronger if the original anchor is core drilled out, the hole scarified, and a new anchor placed in the same location. That is also a technique that withstands the test of time better than just putting a bolt farm very close together -- you won't be able to hide them after enough iterations...

Did you read the previous thread that is linked to above? From my experience testing in all kinds of rock I'm confident that if the original bolt was long enough and one follows my recommendations the new bolt will be adequately strong, I don't tell people things are safe if they aren't.

The video guys stuff is rarely scientific, they'll tell you that themselves. It was a follow-up to help people who don't read.

To make things clearer, the mode of failure in radial tests in softer rock (if the bolt doesn't fail first) is the bolt bends, progressively crushing the rock or the resin below it until the pull-out strength of the remaining resin is no longer sufficient and the resin bond fails either to the bolt or the rock.

In granite with a compressive strength of ca 170N/mm² the resin crushes first, progressively along the bolt as the force increases until something fails.

With the standard concrete test blocks (50N/mm² compressive strength) the resin is actually stronger (60N/mm²) so both the resin and the bolt cut down through the rock until failure. 

Correspondingly we can assume in softer rock that any extra hole will have no weakening effect and in fact any extra hole/resin will artificially increase the bond area and therefore make it stronger.

So I grabbed a conveniently weak test block from aerated cement certified at 4N/mm² so vastly weaker then any rock we climb on and placed three 6mm rod x 100mm long bolts using vinylester resin. Radial tested.

 Standard bolt placement max force 3.46kN. Bolt bent and cut down through the cement until only about 4cm was holding.

Double hole, lower hole resin filled 3.84kN. As expected the extra resin below the bolt effectively created a much larger bolt which resisted bending and cutting down until the last resin failed.

Double hole, lower hole filled with plastic tube 4.36kN. The last was interesting as the plastic tube was actually stronger than the cement, just flattened out under load increasing the area to cut through the cement and making the placement stronger.

Healthy skepticism is healthy. 

But I have yet to see skepticism of any statement by Ser Titt bear fruit.

Solid. Gold. Straight. Dope.

One of about 2-3 people willing to post here that if you don't believe what they say then the burden is on you to figure it out and understand, not the other way around.

Thanks Jim!

Some photos, after the maximum force when the bolt starts to come out and then removed.

Standard placement;

Double resin hole;

Plastic tube hole;

Fascinating! Thanks for sharing your testing.