Thanks for all the info, Rick. It's greatly appreciated as always.
For the metal freaks out there, would the carbon steel bolts be as good at holding the sudden forces imposed by falling as SS? I had the impression that carbon steel was brittle and stainless a little more flexible. Carbon may hold more strength if it's applied evenly, but we're talking about shock forces here.
Muir Madness
They already have that for cracked concrete. It's simply called epoxy injection. They use it for cracked foundations, cracked prestress bridges, etc.Saxman wrote:I wonder if it would be possible to drill a hole, insert a temporary device which would leach a chemical or adhesive which would absorb into the microscopic pores of the rock thereby hardening it and making it more resistant to shearing? One could then insert the bolt in the rock and the rock, at least in a small region around the bolt, would behave like a harder stone. I am sure there are epoxy formulations which could do this and not adhere to the metal or plastic applicator. Hmm, anyone know a patent attorney?
Carbon steel (grade 8) is stronger initially than stainless, but grade 5 is pretty comparable. Here's a chart of bolts with some numbers: http://www.boltdepot.com/fastener-infor ... Chart.aspxmarathonmedic wrote:Thanks for all the info, Rick. It's greatly appreciated as always.
For the metal freaks out there, would the carbon steel bolts be as good at holding the sudden forces imposed by falling as SS? I had the impression that carbon steel was brittle and stainless a little more flexible. Carbon may hold more strength if it's applied evenly, but we're talking about shock forces here.
For sudden forces you're looking at yield strength, the amount of energy required before a bolt will begin to permenantly deform. Once it deforms, although it may not be ready to fail, it needs to be replaced. Ductility is a measure of how much it will deform before breaking. The breaking point is the ultimate tensile strength.
Speaking of the old bolts which some people say need to be replaced. Would it be a liability for those routes to get some sort of note in the online guide? I have seen pictures of what is not safe but that is no substitute for someone with tons more experience letting others know. Is there such a large grey area between statistically improbable to fail and statistically probable to fail that these judgements couldn't be listed?
The theory of evolution is just as stupid as the theories of gravity and electromagnetism.
The epoxy injection makes a mess and is very expensive. You have to completely cover the area you are working on with a sealant cover. The cover has injection and ejection ports. You would get just as good of results with simply glue in anchors. Just don't use the type where there is a packet of epoxy that gets mixed up with the anchor. They are junk. Buy the epoxy separate and apply liberally within the hole and then place the anchor. We have found that works best in concrete. The problem with expansion anchors in soft rock is the point loads upon impact due to a less than perfect fit. The epoxy fills the voids and helps distribute the loads to the rock better. Epoxy gives you a little more safety factor in soft stone.
When the weather moderates, we will be testing the strength of several different types of glue-in anchors in Corbin Sandstone crags. Two of the adhesives to be tested are epoxy and acrylic 2-part mixes that are designed specifically for securing metal rods (re-bar and threaded) to concrete and natural rock.
Preliminary (!) testing in my basement with Redhead anchor adhesives (acrylic ampoules and epoxy mixes) in chunks of RRG sandstone resulted in several observations:
1. Neither the epoxies nor the acrylic adhesives penetrated the sandstone more than about .025 inch. In most cases, this was about .010 inch. Even acetone-thinned epoxy (water consistency) did not penetrate more than about .040 inch.
2. When a stainless steel 3/8-16 304 threaded rod was glued into a .438 dia. hole to a depth of 3.75 inches and then pulled axially (straight out), the failure occurred in shear between the adhesive-impregnated rock and the virgin rock. Neither the threaded rod, nor the adhesive adhering to the bolt threads failed. The threaded rod came out with a cylinder of adhesive-impregnated sandstone surround the threads. This is also the same result found by others who tested threaded rods glued into sandstone, with the exception noted in point 3 below.
3. When the threaded rod was pulled axially to failure, a couple times a roughly conical shaped piece of rock broke away, around and including the entire rod. The failure in these cases was due to tensile failure of the rock.
4. The compressive and tensile strengths of Corbin sandstone vary widely. Variations in hardness are well known to route developers in the Red. In one place the bit advances quickly; in another location, perhaps 2 feet away, it is like drilling into granite.
5. The chunks of rock I've tested so far are only a small sampling of what's down there. And, I'm really weary of totin' boulders outta that Valley! It will be much better when we can use our hydraulic bolt destroyer on real rock walls.
It would not be wise to suggest that a single type of rock anchor would suffice for all RRG bolting. After testing, it seems probable that several different types of rock anchors will be suggested for different types of rock and wall configurations. For an example, in one location, a 1/2x3.75 sleeve anchor might be suggested, and in another location (perhaps a steep overhang) a 6-inch long 3/8-16 threaded rod glued in might be a better choice.
Just some food for thought.
Rick
Preliminary (!) testing in my basement with Redhead anchor adhesives (acrylic ampoules and epoxy mixes) in chunks of RRG sandstone resulted in several observations:
1. Neither the epoxies nor the acrylic adhesives penetrated the sandstone more than about .025 inch. In most cases, this was about .010 inch. Even acetone-thinned epoxy (water consistency) did not penetrate more than about .040 inch.
2. When a stainless steel 3/8-16 304 threaded rod was glued into a .438 dia. hole to a depth of 3.75 inches and then pulled axially (straight out), the failure occurred in shear between the adhesive-impregnated rock and the virgin rock. Neither the threaded rod, nor the adhesive adhering to the bolt threads failed. The threaded rod came out with a cylinder of adhesive-impregnated sandstone surround the threads. This is also the same result found by others who tested threaded rods glued into sandstone, with the exception noted in point 3 below.
3. When the threaded rod was pulled axially to failure, a couple times a roughly conical shaped piece of rock broke away, around and including the entire rod. The failure in these cases was due to tensile failure of the rock.
4. The compressive and tensile strengths of Corbin sandstone vary widely. Variations in hardness are well known to route developers in the Red. In one place the bit advances quickly; in another location, perhaps 2 feet away, it is like drilling into granite.
5. The chunks of rock I've tested so far are only a small sampling of what's down there. And, I'm really weary of totin' boulders outta that Valley! It will be much better when we can use our hydraulic bolt destroyer on real rock walls.
It would not be wise to suggest that a single type of rock anchor would suffice for all RRG bolting. After testing, it seems probable that several different types of rock anchors will be suggested for different types of rock and wall configurations. For an example, in one location, a 1/2x3.75 sleeve anchor might be suggested, and in another location (perhaps a steep overhang) a 6-inch long 3/8-16 threaded rod glued in might be a better choice.
Just some food for thought.
Rick
We cannot change the cards we are dealt, just how we play the hand. - Randy Pausch
None are so old as those who have outlived enthusiasm. - Henry David Thoreau
None are so old as those who have outlived enthusiasm. - Henry David Thoreau
The one bolt failure I witnessed at roadside was due to the rock crumbling below the bolt. For the most part it was a horizontally placed bolt in soft stone. The bolt literally sliced through the stone below it. My point is that a longer epoxy bolt would work a little better in that instance. The expansion bolt put a huge point load on the outside bottom edge of the drilled hole in the rock upon loading. The expansion bolt is only bearing on the bottom middle portion of the bolt. Where as, if epoxy was used, it would distribute the load further out to the width of the bolt and give a little more safety factor. You are doubling or tripling the surface area in contact and reducing the pressure on the rock. A bigger diameter bolt also does the same thing.
Many others agree with you.TradMike wrote:... The expansion bolt put a huge point load on the outside bottom edge of the drilled hole in the rock upon loading. The expansion bolt is only bearing on the bottom middle portion of the bolt. Where as, if epoxy was used, it would distribute the load further out to the width of the bolt and give a little more safety factor. You are doubling or tripling the surface area in contact and reducing the pressure on the rock. A bigger diameter bolt also does the same thing.
All the tests I've seen show glue-ins to be superior in strength to expansion (sleeve) type bolts. I understand in Europe, glue-ins are becoming the preferred rock anchor on all types of rock.
One significant disadvantage of glue-ins is the manner of failure. An expansion bolt, when loaded axially, slowly grinds its way out of the hole. If such a bolt starts to work its way out of its hole on a rock wall, a climber will notice a loose hanger long before the bolt completely exits its hole. Proper re-tightening can bring the bolt back up to snuff.
However, when a glue-in rod failed in several of my tests, it failed totally and in an instant. The glued rods just popped out with no warning. Having a glued-in bolt pop on a 20-foot whipper could spoil one's day. Fortunately, bolts are rarely pulled axially (outward) with the forces I was applying.
It is reassuring to note in the S. Africa and Australia sandstone rock anchor tests, that even in those cases where anchors failed at relatively low axial loads, when they were subjected to downward loads, the UIAA-certified hardware failed before the rock gave way. Most of the bolts on climbs in the Red are substantially perpendicular to the greatest loads that they are subjected to. In other words, we yank more downward than outward.
Rick
We cannot change the cards we are dealt, just how we play the hand. - Randy Pausch
None are so old as those who have outlived enthusiasm. - Henry David Thoreau
None are so old as those who have outlived enthusiasm. - Henry David Thoreau