Tree anchors expressed in kilonewtons

[peds]

Maybe someone here can put some numbers on this, even if it's just anecdotally. 

 

In terms of kN, how much sideways pull, from a theoretically-indestructible sling or chain around the base, can a tree take before it keels over? A wrist-thickness hazel, your average sycamore, a 5ft oak?

 

Has anyone done rigorous destruction testing on this, are there any studies available? Has anyone here yanked an escaped leylandii out the ground with a tractor? Has anyone ever lifted a Toyota Corolla out of a stream using a 27-to-1 haul system on a great big beech tree?

 

Obviously soil depth and quality plays a huge part, maybe even things like recent weather conditions, soil humidity, prevailing wind direction, direction of pull...

 

I'm setting up a rope rescue demonstration for a national meeting of mountain rescue personnel, including a bit on anchor selection and redundancy, using trees, rock gear, and hedgehog ground spikes, and how your 22kn sling doesn't mean much if it's wrapped around something that breaks at half a kN. The rock gear we use is rated for anything between 3 and 30kN, and it'll often be the damp and brittle rock that fails here in Ireland before the cam or nut, and the hedgehog ground spikes we use are only as good as the soil they're hammered into. Same with the trees, you can probably tie twenty tiny little saplings together and get a workable anchor,  as long as they are well equalised...

 

So I'm just looking for any kind of experience or opinions on what kind of force the trees you'd tie up to make a decent anchor can take before they fail. I think it's safe to assume that a single great big oak tree in good soil would comfortably exceed the 25kN target for a rope rescue system, but thanks to redundancy concerns you'd still want to tie at least two together, just to be safe...

 

Anyone want to pluck some numbers out of their orifice, or describe some of the weights you've hung off of trees before? 

 

Cheers dudes. 

[AHPP]

In before the vertical Volvos.  

[peds]

Volvo XC90 at 2700kg, or 27kN, assuming a static load. What's the smallest tree you'd lower one from?

 

 

Edited February 25 by peds

[Dan Maynard]

I assume you're talking sideways pull on the base of a tree, so effectively pulling the whole rootball out at once?

 

I winched my trailer out of a muddy field up a 30 degree slope, so guess 10kN, using some scratty hawthorn hedge opposite so I'd say any decent tree say 6" will be fine.

 

I would consider the area of rootball, and compare that to a steel ground anchor. The tree is relatively shallow but very wide so quite an area to break out.

 

I guess another factor is how well rooted, if the tree is more than say 10 feet tall it must have strong enough roots to withstand the wind loads.

[Rich Rule]

https://youtu.be/ExlaAnSkEq0?si=VKHXVeU-PiYf1PdY

[peds]

30 minutes ago, Rich Rule said:

https://youtu.be/ExlaAnSkEq0?si=VKHXVeU-PiYf1PdY

Shame it was vertical on the tree and not a horizontal load, but still wildly interesting. Love a bit of destruction testing. 

 

From a technical rope rescue point of view, that tree would probably exceed the 25kN target for a system... but you'd still want a second one nearby, just in case. Good old redundancy. 

 

 

[peds]

43 minutes ago, Dan Maynard said:

I assume you're talking sideways pull on the base of a tree, so effectively pulling the whole rootball out at once?

 

I winched my trailer out of a muddy field up a 30 degree slope, so guess 10kN, using some scratty hawthorn hedge opposite so I'd say any decent tree say 6" will be fine.

 

Yeah sideways pull at the base. It'd be interesting to consider a downward pull on a limb or the stem from a redirect, aiming to haul a load out of cave or a river gully though. Wrist thickness or more for climbing on (depending, of course, on so many factors), so two wrists for a rescue load, times it by ten for a safety margin... twenty wrist thickness? 

 

I don't have the arb rigging experience of a lot of people here, so what thickness of wood is the minimum for dropping a 250kg chunk from up in the tree? Probably want to let that run for a bit I guess... 

 

Back to the ground anchor, I'd say a 6" minimum stem  is a decent diameter to aim for and I'm sure it'd perform just fine on its own, personally I'd want three of them tied together though. 

[peds]

Provided the 5 lucky chosen trees can each take 16kN of pull, they are stronger than the anchor cord holding them together, and they only need to give 7 or 8kN each to beat the current weak point in the system, the ropes themselves. 

 

 

 

Maybe we'll track down a load cell and a tractor and try pulling some trees ourselves, it'd be fun to get some numbers on it.

 

[AHPP]

No clicking pulleys. For shame.

 

Wanted a load cell for ages. Bought a GRCS recently. Want one even more now. 

[peds]

Those Clutches do all the clicking for us. Such a pleasing noise!

 

I would like to upgrade the pulleys in the future, but it won't be for clicky ones, just the Petzl SpinL1/2, or another brand equivalent. I definitely see the appeal of the one directional ones, but they wouldn't really help us out I don't think. 

 

Can't afford clicky pulleys anyway, we are getting another pair of Clutches soon enough...