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I have a large piece of rock in my yard. Well it's massive. Over 14 feet long and 7 feet tall. I am guessing it is limestone. Maybe granite. Either way I only have one spot for a slackline and I would like it to mount to the rock safely. The rock is backfilled on one side so I cannot place anything around it.

So far I have found rawl bolts and stainless steel bolt hangers and a properly rated carabiner. Are those suitable to be outside in weather 24/7? I want this to last for years and years. (Just the anchors, slackline will be removed) Rawl bolts are also typically used in climbing where they see force going perpendicular to the bolt, whereas a slackline would be all pull force parallel to it. Are rawl bolts good for that?

Looking for alternative suggestions as well. Ideally it would have a fail safe mechanism so if the bolt ripped out you wouldn't have a piece of metal launching at you very fast. Like a separate anchor point in the ground next to the rock attached to a chain where if the anchor failed the chain would catch it. For rawl bolts it would be able to catch the bolt hanged and carabiner, but if the bolt itself was pulled out there would be now way to stop it from flying across the slackline.

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    The farther around the rock you can move the anchor point the more you shift from the load pulling the anchor straight out to pulling at a right angle. An angled hole will also shift the load vector. Various arrangements with two (or more) anchors, e.g. two bolts angled away from each other and joined with a sling, can also help if properly configured. Granite is a lot harder than limestone. – HABO Mar 24 at 2:08
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Bolts for climbing use can accept forces in any direction. Otherwise bolting in steep overhanging roofs would not work. So simply drill some holes and place your bolts. When connecting bolts make sure that the angle between strands from the center point to the bolts is small, at maximum 60 degrees, better smaller. Otherwise the force per bolt will increase a lot. This also limits how far apart you can place your bolts.

One more notice on the equipment. For the carabiners use steel carabiners not the alu carabiners common in climbing. Fatigue resistance of alu is far worse than for steel. Also avoid to reuse your alu carabiners for climbing once they have been used in slacklines for the same reason.

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  • Are you suggesting using multiple bolts? How would you arrange them and how would you then connect them to a carabiner? I am not a climber so I am new to all of this. – ACD Mar 25 at 15:11
  • If you are just 30cm above ground, 1 bolt may be sufficient. If it fails, you won't fall far. However, people typically use multiple bolts and would connect them with a sling or a piece of cordelette. See this for examples: outdoors.stackexchange.com/a/6857/17053 – Manziel Mar 25 at 15:18
  • My biggest concern is not falling. It will only be a couple feet off the ground. The biggest concern is that it fails and the bolt rips out and flies towards you like a bullet. That is the thing I want to prevent most. – ACD Mar 25 at 15:22
  • In this case it helps to have multiple bolts connected with a shortish piece to a centerpoint. If it is 50cm, any piece in case of an anchor pull will only fly 1m before it is stopped. However, if the anchor is set correctly, there is little risk of an anchor pull. – Manziel Mar 25 at 21:47
  • @ACD search for "top rope anchor" to get an idea of how climbers deal with anchoring to multiple points – njzk2 Mar 27 at 23:25
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Put any bolts as far apart as you can. I would put 4, one at each of the cardinal points for example, or perhaps in pairs of two to the left and right, one on each side higher up, one lower down, then connect lines from each to the one diagonally opposite to form an X shape. Run your slackline from the centre of the X. I would possibly use wires rather than rope for this bit.

This configuration will allow tension on the lines approximately perpendicular to the bolt, and if one breaks, should not cause the bolt to go flying at you. It will also allow a sort of constrained centering of the slackline, so that it can't drift too much in any direction, as a single line between 2 bolts would allow. You will need to protect the ropes/wires forming the X from the rock to prevent rubbing and failure of the rope/wire.

Also make sure you protect the tree - use strapping appropriate for the tree so that you don't damage the bark and accidentally kill it.

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No imaging skills here, but easy to envision. Run the securing line over the boulder and attach it to a suitably long ground spike pounded into the earth. Cover the boulder where the line makes contact, to remove abrasion concern. Add a guide spike hammered into the boulder, one on each side of the line to prevent it from slipping off.

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Coming at it from a construction perspective I would put in epoxy set lag bolts, on on the back side on on the front. Both have an eye. Both have a biner. Rope ties to front biner, is clipped through rear biner, then is clipped through front biner thence to tree.

The rear biner keeps the loop from falling to the base of the rock. The front biner is being pulled sideways by the wrap around end, and being pulled sideways and forward by the rope passing through. If the front anchor fails, you have a few inches extra slack, which drops you down a bit. If the back anchor fails the back rope moves around some.

Another way is to wrap a rope around the base and secure with a bowline. Put a biner at the chosen distance from the knot. Run a rope over the rock and fasten to your anchor on the back.

This one has no forces trying to pull the anchor out. You do have wear on the lasso rope on the rock. Pad?

A third way is to go to your local landscape rock store and ask what they use for anchors in rocks. I suspect it's a big eyebolt and either epoxy or concrete mortar.

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Girdle.

girdled rock

Wrap your rock with a sturdy rope. Attach slackline to rope with carabiner. Or tie it.

Benefit: you don't need to mess with the rock.

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  • I didn't show this due to mspaint skills but the rock is backfill on one side. There is no way to get anything around it, picture the entire right side filled with dirt up to the very top. – ACD Mar 23 at 23:32

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