Replace 3” by 3/8” bolts with 5” by 3/8” bolts?

I can’t recall if this has been asked before, but someone asked me why I dont just use longer 3/8” bolts after extracting the old one (rather than drilling it out to 1/2”). Drill it down a couple extra inches and get the expansion cone and sleeve into “virgin rock” with a 5” long bolt instead.    Thoughts? 

Why? In perfect hard rock it should be fine in theory.

Slipping in a glue-in or 1/2" mechanical bolt is certainly the high road over using a mostly blown out chopped bolt hole.

It would spare the cost of either buying a new 1/2” hanger or the fuss of drilling the old hanger out to 1/2” as well.  I’m certainly not planning on changing my MO of upgrading to 1/2”, which I’ve done with several old routes already, but the question isn’t really “why do it”, but rather “is it possible”. 

More inportant to me is the quality of the hardware. I would rather clip a KB3 or 5 piece in 3/8 than a junk 1/2 inch wedge. Or sleeve.

And even if the hole is compromised  going deeper will fix it. 

In my experience spinning does not compromise the hole in hard rock.

In quartzite i have pulled a number of 3/8 Rawl drives (compression bolt) and after correcting depth a 3/8 5 piece fit perfectly.

It is certainly possible and can work very well, depending on the rock and the condition of the hole of course. I've also drilled out 3/8" to 10 mm in good rock (~.020" bigger) and it always worked well, but that is another topic and probably controversial.

I think an important consideration that hasn't been discussed and that doesn't get nearly enough attention in north America is thinking about how to preserve the same bolt hole for the longest period of time possible. Climbing may be a new sport but it's going to be around for a long time. If you can get another 50+ years from a 3/8s bolt hole you're extending the useful life of that bolt hole. People act like 50 or 100 years is forever. It's quite a short period of time, and if we put a little thought into our actions I think we can make crags have far fewer bolt holes in the not too distant future. 

Maybe this isn't always a good solution, but drilling two new inches of rock and getting the wedge in the good rock sounds pretty bomber generally speaking. 

Depends on how fucked up the hole is, which depends on rock type, original quality of hole, yanking finesse, etc.  For example, on desert sandstone this isn't going to happen. On good granite, maybe.

The minimum embedment length of a 3/8" wedge bolt ranges from 1.5" - 2" depending on the manufacturer, and the additional 2" of depth to take a 5" bolt meets or exceeds this minimum. So that should be ok?

So as long as the hole is not blown out to the point of allowing the bolt to wiggle a lot (not very scientific, I know), it should work? A purpose-built bolt extractor (like the YABR) should leave a pretty clean hole, from my experience.

If any practitioners out there (especially anyone with engineering expertise) can confirm or deny my thoughts on this I'm happy to hear it.  

Ok, here is what I tried:

• install a 3/8" x 3" wedge bolt, torqued to spec
• spin and extract it
• drill 2" deeper and install a 5" bolt torqued to spec
• pull it until it either breaks or comes out (I used a hydraulic punch press with a modified draw stud)

My theory was that if the bolt breaks before it comes out, that's evidence that drilling the hole deeper works.

I did this eight times, and every time the 5" bolt broke. So it seems the idea is sound.

All the usual disclaimers apply, including but not limited to: 

• sample size of eight is pretty small.
• perhaps rock type matters: I tested in good quality basalt
• maybe the brand of wedge bolt matters
• maybe it matters if you use a brand new drill bit vs an old drill bit
• probably a bunch of other things I can't think of right now

Any constructive thoughts or comments are welcomed.

Derek Woods wrote:

Ok, here is what I tried:

• install a 3/8" x 3" wedge bolt, torqued to spec
• spin and extract it
• drill 2" deeper and install a 5" bolt torqued to spec
• pull it until it either breaks or comes out (I used a hydraulic punch press with a modified draw stud)

My theory was that if the bolt breaks before it comes out, that's evidence that drilling the hole deeper works.

I did this eight times, and every time the 5" bolt broke. So it seems the idea is sound.

All the usual disclaimers apply, including but not limited to: 

• sample size of eight is pretty small.
• perhaps rock type matters: I tested in good quality basalt
• maybe the brand of wedge bolt matters
• maybe it matters if you use a brand new drill bit vs an old drill bit
• probably a bunch of other things I can't think of right now

Any constructive thoughts or comments are welcomed.

I'm guessing what matters most is if the edges of the hole after a well used old bolt has been pulled. Are they chippped/is the hole wallowed out? Might introduce movement that wouldn't be there if you drilled out to 1/2".

There is a lot of testing and replacement literature from ASME, US regulatory agencies and anchor manufacturers that support that method of replacement. The basics as far as what you are doing are that the nominal size of the hole can at no point be more then 1.5 times the nominal size of the anchor (meaning in this case that no measure of the hole in any direction should have been enlarged past 9/16" at extraction) and the effective embedment needs to be MORE THAN 3 diameters greater. Installation can still fail because you can't get torque without the bolt spinning or the cone doesn't bite and you can't get it not to pull itself out as you tighten, but if the Installation is good, it should provide confidence to meet the rated load.

Side note: it is entirely acceptable to fix a hole with anchor gout and redrill it after 24 hours and good on you for using long enough anchors that the metal fails before the rock.

Carson Mc wrote:

There is a lot of testing and replacement literature from ASME, US regulatory agencies and anchor manufacturers that support that method of replacement. The basics as far as what you are doing are that the nominal size of the hole can at no point be more then 1.5 times the nominal size of the anchor (meaning in this case that no measure of the hole in any direction should have been enlarged past 9/16" at extraction) and the effective embedment needs to be MORE THAN 3 diameters greater. Installation can still fail because you can't get torque without the bolt spinning or the cone doesn't bite and you can't get it not to pull itself out as you tighten, but if the Installation is good, it should provide confidence to meet the rated load.

Side note: it is entirely acceptable to fix a hole with anchor gout and redrill it after 24 hours and good on you for using long enough anchors that the metal fails before the rock.

That's good information, thanks!