Here’s another “tres bien” video from ENSA (the French National Guide School) where they take engineering tools out into the real world and see how climbing gear and technique really work.
(If you haven't seen it yet, be sure and watch this other great video, where they test the usefulness of brake knots in the rope for two person crevasse rescue.)
In the mountains near Chamonix, they rigged some pull tests on all manner of snow anchors, some traditional (pickets, snow bollard, ice axes, vertical and horizontal skis), and some unconventional (plastic bags, soda bottle).
Here are some takeaways:
Placing a vertical anchor, like a picket, at a 25° angle leaning away from the direction of pull makes the anchor approximately 40% stronger. (See graphic below.)
Even in a buried plastic bag and a soda bottle held 200+ kg, more than enough to rappel from. (I still think I'd let my friend go first . . .)
There’s a nice chart near the end that summarizes all of the data. (The fourth column, “strength in daN”, means “dekanewton”, a metric unit of force. It's 0.01 kN, or approximately the same as 1 kg of force.)
Unfortunately, I can’t embed this video on my webpage, so you're gonna have to go to YouTube and watch it there.