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Mighty Hiker
climber
Vancouver, B.C.
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Nov 21, 2009 - 11:53pm PT
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"critical" spacing between 2 bolts is 2 imbedment depths for full strength
or
"minimum" spacing of 1 imbedment depth for 50% strength That may be the nub of the issue. I read 'critical' to read "absolute least" - and that's probably assuming good rock quality, reasonably dense and uniform, without nearby weakness. In other words, best case, with the bolts correctly placed. And a lot of bolts aren't in best case scenarios, or quite properly placed. And I read "minimum" to mean "if it's physically impossible to place them farther apart" - the half a loaf thing.
It would be interesting to know the science behind their recommendations. It may be based on pulling bolts out of some sort of cast material, which may not quite be real world.
With 'standard' bolts being 2.25 or 2.5 inches, the conclusion I draw from Clint's information is that belay bolts should at the very least be five inches apart, and five inches from any visible weakness - and probably considerably more. For longer/fatter bolts, farther. There don't seem to be any negatives from this, and there are also non-safety positives, such as spreading out climbers at hanging belays a bit.
This is not criticism of Steve, Clint, Joseph or anyone else here - I'm sure you all take care to place sound belays, having regard to needs and the environment. But many belay anchors, especially at sport climbing areas, don't meet the critical and sometimes not even the minimum (strength compromised) spacing. The rock in such areas (Skaha, Cheakamus Canyon, Vantage, Smith, etc) also tends to be less sound than granitic rock, although the latter has its own issues.
I certainly use such belays, and they're much better than none, but the relatively few bolt belays I've placed are comfortably spaced. It appears that a bit more knowledge and education about this subject might be useful.
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WBraun
climber
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Nov 22, 2009 - 12:11am PT
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You gotta be kidding us Anders.
Are you really trying to insult us.
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Mighty Hiker
climber
Vancouver, B.C.
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Nov 22, 2009 - 12:22am PT
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Far from it. I'm genuinely interested in the subject of the appropriate, safe placing of belay bolts. It appears that many may be placed too closely, having regard to recommended spacing and the characteristics of the rock they're in, and that that reduces their strength and perhaps safety. I would like to learn more about this, beyond the purely empirical and anecdotal, and maybe there is something we can all learn about the subject. Perhaps there is even some objective information about it - testing and such.
There may be other things that are more pertinent to climber safety, allowing for there being no such thing as safe climbing. But belay bolt spacing and placement is something I've often wondered about.
What are YOSAR practices in these matters? Different needs, of course, but what size and type of bolts does it use, and what spacing?
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Slater
Trad climber
Central Coast
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Topic Author's Reply - Nov 22, 2009 - 12:30am PT
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I don't mean to take the head in the sand approach, but none of the anchors I've set, or ever used (to my knowledge) have ever blow. Of course now we're gonna see the pictures of blocks of rock sitting at the base with bolts in them... or accident reports of bolted anchors blowing...
(actually, curiosity has gotten the better of me... let's see 'em- never to old to learn).
Putting two bolts closer than 5" just seems pretty idiotic, so does bolting near an edge. And nobody (using the term "nobody" loosely because there is always an exception to the rule but they're such morons nothing is gonna change that) puts in anything less than 3/8" anymore. And two bolts is redundant, which is more than the single bolts that typically save our sorry a$$e$ on a regular basis.
All that said, all this is good for discussion and keeps us sharp and is overall good reinforcement. Put 'em in right, use the best materials available.
But I kinda think that if a piece of rock with two bolts in it blows, it's just your number is up. Like surfing and getting hit by a shark. It's just out of your hands (barring the idiots who surf in sketchy places like Ano Nuevo (me- can't help it, it's just too good sometimes) etc... sometimes you're just asking for it...).
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Mighty Hiker
climber
Vancouver, B.C.
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Nov 22, 2009 - 12:42am PT
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A website with some information about this: http://www.climbargolis.com/Glue-inBoltDesign.htm
I'm not sure who Bolt Products is, apart from being German, but there is an enormous amount of interesting information about bolting and safety at the link.
Edge Effect.
If a bolt is placed too near the edge of the piece of rock or near a crack/fault the loading of the bolt will cause the rock to break out in this direction at a relatively low load. There has been much research into this and the general recommendation is not to place a bolt within 200mm of the edge, some go as far as 400mm. Unfortunatly when using the staple type of bolt the action of drilling a second hole creates this edge and the cones of failure overlap, seriously reducing the load bearing capability. The fastener company Hilti recommend a hole spacing of twice the hole depth for adjacent fasteners to avoid this problem. ITW Ramset give a hole spacing of 1.5 x depth as the critical spacing and a distance of 1.25 x depth from an edge. The UIAA recommend a spacing of at least 200mm when fitting two bolts at a belay. I couldn't find the direct reference on the UIAA website. However, their minimum recommended spacing is 20 cm. Hilti goes with "separated by twice the depth", but also "20 cm from an edge/crack". Perhaps the UIAA and the climbing-specific industry are more conservative.
I wonder what else might be out there? Perhaps not in English? There may be more research into this in German.
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GBrown
Trad climber
North Hollywood, California
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Nov 22, 2009 - 12:59am PT
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I swear -- when I first saw this discussion topic, I thought it was about who was the best anchor person on a news show about rap music.
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WBraun
climber
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Nov 22, 2009 - 01:07am PT
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Anders
If you want to learn more start climbing.
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cragnshag
Social climber
san joser
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Nov 22, 2009 - 01:12am PT
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Here what I use for most of my rap anchors (similar to Kev's set-up): 316 SS 5/16" quick link to a 316 SS 3/8" chain link. Pricey items, the 316 SS... even at concrete industry wholesale this set-up (2 quick links, 2 chain links) costs me over $15. But they will never rust away in non-chloride inland areas like Yosemite.
For less than $5 you can get the above anchor in carbon steel. And even the hardware grade stuff is plenty bomber- it does rust, but there is so much steel cross-section that it would be a long time before the diminished strength due to corrosion would be an issue. And when it does, it is easily replaced by another inexpensive link.
Granted the above system is not so convenient as the hooks or other clip-in anchors, but are great for more obsure locations that don't see a lot of traffic (so you don't need to worry about rope wear-through).
As to the question of spacing the anchors, I can relate to feeling wigged out when seeing two anchors placed really close together- it FEELS like it is just one anchor and non-redundant. However, in reality, it is not an issue in most rock. In the concrete industry we always design our steel-to-concrete connections based on the shear cone of the Nelson stud or expansion anchor. This "shear cone" is the conical piece of concrete surrounding the anchor that breaks free from the base wall or block. The pullout strength of an individual anchor is the concrete shear force (a function of the compressive strength Fc of the concrete) per square inch times the surface area of that cone. The deeper the anchor, the taller the cone- and thus more surface area of shear resistance. We regularly design huge plate steel connections that consist of 6 or 8 studs spaced per manufactures specs (see Powers example that Clint posted earlier). Keep in mind that the pullout values for the anchors are cited for concrete with the shear cone as the controlling factor. In reality, most rock is way stronger than concrete, thus manufacturer provided pullout values are lower than what you would experience in good rock. In fact, I'm guessing the controlling factor in good granite (Fc= 12,000+ psi compared to standard concrete Fc of 3,000-5,000 psi) is the cross-section tension strength of the steel.
If the rock is fractured, then you reduce the cross-sectional area of the shear cone by the area of the fracture in the vicinity of the anchor. You can also treat the rock fracture as an "edge" and reduce the anchor strength per manufacture "edge distance" factors.
All of the above is for tension (pullout) of an anchor in concrete or rock. Most falls on bolts will have a combination of tension and shear loading on the bolt itself. The given shear strength on the bolt itself controls for shear force that the anchor experiences and is the same for a two-bolt anchor regardless of the bolt spacing.
Long story short, if you see two bolts real close together, don't fret, physics is on your side. Unless the rock is fractured in several places, you be fine. It just looks scary.
Of course it would be nice if folks refrained from putting anchors at the "minimum" spacing since the end user has enough things to fret about...
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Mighty Hiker
climber
Vancouver, B.C.
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Nov 22, 2009 - 01:27am PT
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If you want to learn more start climbing. Yes, sir! Sergeant Werner, sir! Good idea, but I already did, long ago. And I still do some climbing, though not as much as I'd like. I've even clipped some bolts, and placed a bunch. Maybe we can go climbing together during the FaceLift next year, or in the spring if I'm down that way. That would be fun! Or you could come to Squamish - you'd love it. In summer.
And yes, I'll install the SuperTopo filter on my computer, and try not to work quite so hard.
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bhilden
Trad climber
Mountain View, CA
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Nov 22, 2009 - 03:14am PT
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Cargsnhag and Clint,
I think it is important to mention that for most rock climbing applications, the 'shear strength' is more important than 'pullout strength'. The Powers
Specs that you both talk about appear to be most concerned with 'pullout strength.'
I would be interested to know if there are any recommendations for hole spacing with respect to 'shear strength.'
Bruce
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Clint Cummins
Trad climber
SF Bay area, CA
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Nov 22, 2009 - 03:58am PT
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Thanks, Bob. I like the stress cone diagrams. It makes it fairly easy to visualize why the 2 times imbedment depth keeps the cones from overlapping, so they retain independence/full strength.
And I like the compression strength rating for good granite.
It wonder how much it varies for the "grainy" granite.
I have drilled 3/8" by hand in concrete, and it didn't go all that quickly, so that makes me wonder.
Bruce,
I left off part of the description for the bolt spacing from the Powers PDF. The loading was for "tension and shear" for the 2x depth and 1x depth specs. (So I put those words in just now in an edit).
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JimT
climber
Munich
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Nov 22, 2009 - 05:21am PT
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Speak of the devil and he will appear (I am the owner of Bolt Products and English to boot)!
Interesting thread and still suprisingly polite so here are a few observations from a lot of research and testing.
The monster setup from Steve Grossman:-
Technically it is undesirable to re-weld the old chain welds BUT using that size chain you donīt really need to weld at all anyway so carry on! This is only of concern at the loads we work at when you get down to 6mm/ 1/4" chain.
Leaving the weld discolouration is also undesirable as this promotes corrosion, better is to pickle the welds afterwards and preferably passivete as well. However as above, in this size of chain I wouldnīt be worrying about it either. Keep up the good work.
Placing two seperate rings/rap hangers/karabiners/whatever:-
If the two points are long enough that they can swing and touch together under load then this is o.k. but if the cannot touch then there are two problems. Firstly they twist the rope which for rapping isnīt such a problem but when lowering on sport routes is a pain, secondly the wear on the points is considerably faster as they vibrate quite a bit as the rope weak passes over. At a rough estimate the wear is about 30% higher.
We normally recommend (and usual practice in Europe) is to set the ring etc about 45° down from the other.
Bolt depth and spacing:-
In Europe the wedge (or through) bolt are the universal bolt and these comments ONLY cover this type of bolt. There has been virtually no testing here on the 5 piece type.
There has been some controversy about the recommended depth, with the UIAA trying to push through 7cm/7 X diameter but this has failed as the manufacturers of the bolts temselves are adamant that 5 X the diameter is adequate. This is the requirement of the European Technical Approval to which they are tested by the manufacturer, the bolts are then bought in by climbing equipment manufacturers and tested to EN959 for resale. 5 X dia (that is 50mm embedded depth for the standard 10mm bolt used here) has proved time and again to be adequate. To allow for the nut, hanger, a bit of pull out when tightening etc the usual choice is an 8cm bolt, the next shorter commercially available bolt is 6cm which is cutting things a bit fine though on the hard granite these are sometimes used to save drilling.
The spacing recommendations are generally extremely conservative as they are based on concrete tests which work out a bit different from solid rock.
However to conform to the bolt manufacturers own certification we (and everybody else) just say 200mm to save a lot of confusion. Personally I generally place at a minimum of 230mm because that is how far it is from the tip of my thumb to little finger. As mentioned, further apart reduces the chance of hitting a fault in the rock.
The cones of fracture stuff is interesting and there is an endless amount of research done on this for the construction industry but in all our testing (and weīve done plenty) this rarely is what we see. The bolts are designed for maximum performance in medium to strong concrete which is in climbing terms a pretty weak bit of rock. In real rock there are two possibilities, in harder rock the bolt breaks before the rock and in weak rock the bolts pull through and cannot impose enough force to cause rock failure. The only time we have seen the classic cone failure (with mechanical bolts) is in conglomerate when we have have the luck to hit a buried pebble which rips out through the sandy rubbish holding it all together.
Because of the type of concrete used for the standard test the bolts themselves hold better and cone failure is usual but in an equivelant strength sandstone for example the bolt does not grip well enough to cause cone failure.
Bolt size:-
Good quality 10mm 316 stainless wedge bolts hold about 38kN, that is 50% over the requirements of EN959 and a load impossible to achieve with normal climbing equipment, a 3/8 bolt would have absolutely no difficulty in achieving the standard.
Bolt failure mode:-
In both straight-out (axial) pull and shear (radial) the mode of failure is bending shear and there is effectively no difference in the failure load, for EN959 both axial and radial are tested as the required values are different but for practical purposes most people are only interested in the worse case which would be axial. Repeat loading is of little concern until it looks so bad you wouldnīt use it anyway! Hangers are a bit more susceptible to cyclic loading but we are still talking of hundreds of full-on hits.
Drilling:-
All rock are different to drill, one of the biggest differences is the elasticity, the more elastic it is the more the hammer blows are absorbed and hace no drilling effect. Concrete is made of a fairly elastic matrix with extremely hard conglomerate whereas some granites have very low elasticity and very weak inclusions (feldspar for example).
What you need is a drill that varies the hammer frequency to suit the natural elastic harmonic of the rock but I doubt Bosch are working on this one!
In our experience the hardest rock to drill is high quality marble which also destroys drill bits for fun.
Hope some of this helps and now Iīm going climbing!
Jim Titt
Bolt Products
Germany
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Slater
Trad climber
Central Coast
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Topic Author's Reply - Nov 22, 2009 - 12:24pm PT
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Kinda hard to argue with any of that.
But I still wanna see some pics of slabs of rock that blew off with bolts in them. Someone make my day. And tell me the story too if you can. I've had enough engineering mumbo jumbo.
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couchmaster
climber
pdx
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Nov 22, 2009 - 01:26pm PT
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Thanks Jim! great to see actual and real information instead of guesswork. I've perused your site quite a bit especially looking for info on glue ins. We chose to use Wedge Anchors anyway due to ease of placements, but I just wanted to say that your site is a wealth of information, and it's greatly appreciated.
http://bolt-products.com/
One thing which may be of significance is that no one has mentioned the use of a torque wrench for proper installation. It may be an indication that even a 3/8" wedge anchor is so much overkill that even torqued incorrectly there is way too much margin to critically affect the installation. It is even less significant in the 1/2" diameter sizes. BUT, a torque wrench should be utilized to optimize the strength of your placement. Too much or too little is a bad thing. If you put an extension on it, you won't rap your knuckles and can spin it around for an even faster install.
I'm the only climber I've seen running around with one though and bolts aren't falling out of the rock.....
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WBraun
climber
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Nov 22, 2009 - 01:35pm PT
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Man
The guru of anchors and bolting. Awesome web site Jim.
Thanks.
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Hummerchine
Trad climber
East Wenatchee, WA
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Nov 22, 2009 - 01:43pm PT
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Wow, Jim...fascinating stuff! There is some great bolt and bolting info on the ASCA website; this would be a great addition!
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Steve Grossman
Trad climber
Seattle, WA
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Nov 22, 2009 - 01:43pm PT
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Jim- Have you run into any twist shearing issues connected with the threading procedure on stainless steel wedge anchors that are 3/8" or smaller in diameter? What installation torque value are you recommending for tightening wedge anchors.
Those heavy anchors of mine were shown without the muriatic acid pickling and blackening step that would tend to reduce the oxidation/ corrosion at the TIG welds and reduce the glare.
You must be involved in some artificial climbing wall work. What is the CEN using for service load values on protection points these days?
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Greg Barnes
climber
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Nov 22, 2009 - 01:47pm PT
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Back to the computer - try to answer things in order:
 Steve, you are right that 3/8" bolts are not that strong by construction standards, and 1/2" would be minimum size for those standards. But they would just laugh at the concept of 1/4" bolts...and climbers have used how many 1/4" bolts, and for how long? I think you can agree that 3/8" stainless is a lot better than 30 year old 1/4". When we can power drill, 1/2" is the preferred size.
hand drilling 1/2" in granite is a very big deal, at least on good granite. I've hand drilled a lot of 1/2" x 3" holes at Red Rocks, and it can take from 6 minutes (soft white rock) to 20+ minutes. I've hand drilled 3/8 x 2.25" holes in softer Tuolumne granite in 6 minutes, but the same hole on the best Tuolumne granite takes 14 minutes plus, and that same hole on the best Valley granite can take 20+ minutes. Asking rebolters to repeatedly drill 1/2" on good Valley granite is a quick way to reduce the number of rebolters from the current levels (3 or 4 fairly active) to zero (actually Roger would probably do it!). And you can always remove the 3/8" bolts and drill 1/2".
getting an exception to the power drill ban in Wilderness would require that the NPS or other managers officially "manage" bolts (and thus they could get an exception since power drill replacement is less disturbing to wildlife than hand drilling - which is true). This is highly unlikely until some sort of national bolting policies are settled on, and it's probably at least a decade before that happens. Even if the NPS approved it, the Sierra Club and others would most likely sue to block it - not because they care about climbing, but because it would be seen as a foot in the door for snowmobilers and others who want to have motorized access (which is of course a totally different issue). Pushing national managers for an official exemption could even bring about more regulation of bolting - we would have to discuss this in detail with the AF policy folks before going that route.
Werner, if you know who we can talk to in Yosemite, please email me (I've asked you and others before, never got an answer). We could probably get an exception for the Lower Merced areas with just local approval, since those are non-Wilderness. Not that there are many bolts to replace there (except Parkline slab).
Locker, power drills can be used only in the NON wilderness areas of JT, and only with a permit. You can't use them in the Wilderness even with a permit. I'm the one who applied for and got the first power drill rebolting permit in JT - it's definitely only for non-Wilderness.
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Hummerchine
Trad climber
East Wenatchee, WA
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Nov 22, 2009 - 02:03pm PT
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Hey Greg, thanks for the additional info! I'm super curious; what would those hand drilling times be for half inch bolts? I have no idea.
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Greg Barnes
climber
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Nov 22, 2009 - 02:16pm PT
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I've actually considered finding out, especially on East Cottage Dome in Tuolumne. There are a several key bolts that are 5/16" buttonheads with spinning hangers. This is mostly due to rock breaking out behind the hangers. Anyway, if you pull a 5/16" (insert multiple swearwords for even thinking about that...), you can't hand drill a 3/8" in the hole since the bit gets stuck (too close in size). But you can hand drill a 12mm or a 1/2" bolt, and the bit doesn't get stuck.
I did replace a handful of bolts with 12mm Petzl Long-lifes for similar reasons. Namely, replacing Diamond taper bolts in 3/8" holes with 12mm. This is because the taper bolts leave a lead sleeve at the bottom of the hole, and if you try to hand drill through them, the bit gets stuck. But if you drill out the hole to 12mm, the rock stops the bit, and you break off chunks of the lead along with the rock, and it works out fine. Petzl Long-lifes because they are WAY shorter than any other larger bolt option.
The drilling times on those are meaningless though, it's a bunch of light tapping, and most of the rock was gone already.
My guess for a 1/2" x 2.75" bolt in good granite - this is assuming that you are a fast driller with arms in shape for drilling - is maybe 30-35 minutes a hole. Just a guess, and it really depends on the rock quality.
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