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Partial Anchor Failure
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celticelement


Jul 7, 2011, 1:20 PM
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Partial Anchor Failure
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I have been reading a lot about anchors lately.

I hear the tests and the scientific theories which get questioned as being valid in real world climbing scenarios. Then I hear of real world climbing wisdom get thrown into doubt by more tests.

What I have not found yet is some actual instances of partial anchor failure. I am interested in what system did actually hold in the case where other pieces of the same anchor system failed. I would be most interested to know what kind of equalization and redundancy systems were being used.

If there are any of these examples out there I realize there will be all kinds of factors not taken into account. But to hear of something that did work once will give some justification to believe it can work again.


acorneau


Jul 7, 2011, 1:31 PM
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Re: [celticelement] Partial Anchor Failure [In reply to]
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celticelement wrote:
I have been reading a lot about anchors lately.

I hear the tests and the scientific theories which get questioned as being valid in real world climbing scenarios. Then I hear of real world climbing wisdom get thrown into doubt by more tests.

What I have not found yet is some actual instances of partial anchor failure. I am interested in what system did actually hold in the case where other pieces of the same anchor system failed. I would be most interested to know what kind of equalization and redundancy systems were being used.

If there are any of these examples out there I realize there will be all kinds of factors not taken into account. But to hear of something that did work once will give some justification to believe it can work again.


Here is a story as relayed to me by someone I know directly. (Names changed to protect the innocent!)


In reply to:
We rigged a rappel anchor at [XYZ] Wall with 3 pieces of pro . Of course
it was ERNEST. We used it for a couple hours with no trouble other than
re-screwing screw-gates. It was inspected by three instructors when it was
installed and several times during it's use.

While an adult woman 150-200 lbs was rappelling on it, a nut blew out. She
experienced about 6" of extension. The other two hexes held firm. She was
probably 10'-15' from the bottom, so she continued rappelling to the bottom.
We shut down the rappel. No one was injured, and the system behaved the way it was supposed to in the case of a single point of failure.

I put the nut back where it had been, and it was clear to me that the rock
had failed around the nut. In my opinion it was a less than ideal placement
due to poor rock quality. We moved the placement to better rock, inspected
the anchor system again, and continued on without incident.

Is that the type of thing you're looking for?


celticelement


Jul 7, 2011, 2:03 PM
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Re: [acorneau] Partial Anchor Failure [In reply to]
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That is what I am looking for except I would really like to know which way they had that anchor rigged as far as equalization and redundancy. Did they have it all on a cordelet tied for the single direction of pull? (...seems fairly easy to anticipate direction of pull for a rappel anchor.) Or were they using a sliding x configuration? With or without limiting knots?

Edit: I guess there is a good chance they had it rigged like a top rope anchor with all 3 rope/webbing from the pieces being clipped directly by the anchor point carabiners.


(This post was edited by celticelement on Jul 7, 2011, 2:19 PM)


rescueman


Jul 7, 2011, 10:46 PM
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Re: [celticelement] Partial Anchor Failure [In reply to]
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celticelement wrote:
to hear of something that did work once will give some justification to believe it can work again.

You're asking the wrong question.

We learn from failures. The trivial fact that a system
worked once tells us nothing at all about whether it will work again - even in the exact same situation and configuration (which, of course, can never be precisely replicated).


kikitastrophe


Jul 8, 2011, 6:56 AM
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Re: [celticelement] Partial Anchor Failure [In reply to]
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I don't know if this is particularly interesting but I had a 3 piece anchor set up on a multipitch, equalized in one direction via a cordelette with a figure-8. During use the middle piece (a 0.5 C4!) failed while I was bringing up a climber - the master point didn't budge and the other 2 pieces (a nut and a tricam! I <3 Seneca) held securely and there were no ill-effects to the system. This did reinforce my inclination to always be redundant.


chadnsc


Jul 8, 2011, 8:06 AM
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Re: [celticelement] Partial Anchor Failure [In reply to]
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Here is an example of anchor I set a few years ago where a single piece failed due to rock movement.

Anchor components:
1.5 Technical Friend (left piece)
#6 BD stopper (center piece)
Pink Tricam (right piece)

All where rigged together using 8mm static line rigged using web-o-let system (figure eight on each end with a loop for the middle piece).

The master point of the anchor consisted of a figure eight on a bight with two opposite and opposed locking biners.

Mode of failure:
Upon loading the system with a moderate fall of 60 inches the rock containing the pink tricam shifted and the piece blew out.

The moderate fall was caused by approximately 30 inches of excessive slack in the belay.

Upon inspection of the rock it was shown that the car sized horizontal slab was actually balanced on a fulcrum and needed only around 250 pounds to shift the boulder and enlarge the crack the tricam was placed in. This enlargement of the crack by only 1/4" was enough to allow the pink tricam to pull out.


Results:
The remaining two pieces held and the climber was not injured.

When the pink tricam pulled there was less than three inches of extension is the system.


celticelement


Jul 8, 2011, 9:52 AM
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Re: [rescueman] Partial Anchor Failure [In reply to]
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RE: rescueman
In this case we don't learn if the equalization systems work unless we have a partial failure. If there is a total failure all we can say is an alternate system may have worked but we won't know for sure. If a system holds with no problems we have no idea if it was only a single piece that held the entire load or if in fact it was equalizing correctly. And extension will never be an issue when all the pieces hold. It is only in the case of a partial failure that we actually get to see the anchor system in action.

I don't think any example is at all conclusive, but it may be informative.


rescueman


Jul 8, 2011, 10:10 AM
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celticelement wrote:
And extension will never be an issue when all the pieces hold.

Extension is never an issue if we use what the climbing guides in the Northeast US have long been advocating: a cordellete tied in a fixed, focused, pre-equalized anchor system.

Tests have demonstrated that even the sliding X experiences enough friction between 'biners and slings to prevent equalization at the speed of energy dissipation at the anchor.

So, if we want a load-sharing anchor system with no extension, the choice is obvious. A fixed, focused multi-point anchor is the only kind used in rescue scenarios, when lives are literally on the line. Climbers would do well to follow suit.

Edited to add: And I use only nylon cordage and slings, which have much more forgiving qualities than any of the high-strength cords or webbing, always preferring cordage to slings for any but the shortest lengths because of its better knotting and energy-absorbing qualities.


(This post was edited by rescueman on Jul 8, 2011, 10:13 AM)


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