Picket test

[Gary_Yngve]

The problem with in-line or a main and then backups, is that once the first one fails, you've excavated the whole snow wedge in front, and the rear anchors are now totally worthless, if I understand the pdfs correctly.

 

So if you're really concerned, you'll need to build the 2nd far enough away.

 

[korup]

Tonight at Alpental a friend and I did some on-snow picket testing with skis. All the tests were done with a 24" MSR Coyote (no cable, just runners), a 10.5mm rope, and the rope was (unrealistically) tied directly to the anchor. Snow conditions were 3-4" of wet corn/slush, and then more consolidated snow below that, on a slope (Sessel) of 15-20 degrees. Speed at impact with anchor felt like ~25 mph(?).

 

Test 1: Vertical placement, top clip, hammered straight into the snow. Skied 30m of rope. Slight tug on harness, followed by explosive anchor failure, with picket landing ~10 feet from where I stopped downslope, pulling the entire coiled rope with it. FAIL.

 

Test 2: Vertical placement, top clip, ~15 degrees back from horizontal, placed below slush level. Skied 15m of rope, with the same results as above. FAIL.

 

Test 3: Vertical placement, middle ("Sierra" style) clip, ~15 degrees from horizontal, below slush level. A slot for the runner was excavated, and then snow was replaced and compacted. Skied 15m of rope. FAIL.

 

Test 4: Horizontal "deadman" placement, ~2' down, with a trench for runner. 15m of rope skied. Anchor INTACT.

 

I don't have any way to easily estimate the forces involved, but might sacrifice a Screamer if I do it again. The forces were all directed down, and should have pulled the anchor deeper in the snowpack, but they simply ripped straight out through the slope.

Edited May 30, 2008 by korup

[robk]

Test 1: Vertical placement, top clip, hammered straight into the snow. Skied 30m of rope. Slight tug on harness, followed by explosive anchor failure, with picket landing ~10 feet from where I stopped downslope, pulling the entire coiled rope with it. FAIL.

 

Test 2: Vertical placement, top clip, ~15 degrees back from horizontal, placed below slush level. Skied 15m of rope, with the same results as above. FAIL.

 

Test 3: Vertical placement, middle ("Sierra" style) clip, ~15 degrees from horizontal, below slush level. A slot for the runner was excavated, and then snow was replaced and compacted. Skied 15m of rope. FAIL.

 

Test 4: Horizontal "deadman" placement, ~2' down, with a trench for runner. 15m of rope skied. Anchor INTACT.

 

I don't have any way to easily estimate the forces involved, but might sacrifice a Screamer if I do it again. The forces were all directed down, and should have pulled the anchor deeper in the snowpack, but they simply ripped straight out through the slope.

 

Do you know anyone that has a load cell available? It would be very interesting to actually measure the forces and look at the failure modes. If I remember right, the Mountain Rescue Association (MRA) has some load cells available for member teams to use in testing. Not sure who has them now, but you could contact your local MRA team and see if you could work with them to create some new data points.

 

It appears that your results are in line with the work that Fortini, et al have done in this area.

[mike1]

The problem with in-line or a main and then backups, is that once the first one fails, you've excavated the whole snow wedge in front, and the rear anchors are now totally worthless, if I understand the pdfs correctly.

 

So if you're really concerned, you'll need to build the 2nd far enough away.

 

My thinking also. There's also the cross method they mention.

 

Belays on snow has some good info too.

 

UIAA is another good resource for info but they haven't any standards for snow stakes. I've sent them an inquiry and will update here if and when I get an answer as to why.

 

 

Edited June 1, 2008 by Mikester