After a brief hiatus, I’m back and making less sense than ever!
We started work repairing a blowout on the Streamside trail.
Moving rock into the repair area is challenging. There are no clean lines to hang a skyline, there’s no good quary of rocks directly above the site. After a few months of occasional study and lots of pondering, I realized there is no good solution, just some solutions that are slightly less bad than others.
We got to work on the first least bad option this week. The good news is we partly cleared a landing to stage rocks. And learned some stuff. So that’s nice.
Learning 1: Tripods in a boulderfield may cost more time than they save. We were really confined to placing tripods on a few flat-ish surfaces, and 4×4’s really like to skid off of polished river rock. In short, there was a lot of slip sliding tripod adventure. We got some rocks across the creek, which is good.
Learning two: Sometimes reading the grain of a rock really works. Really really. I saw how this rock was splitting in other spots, and with minimal wedges made a nice 3′ x 3′ split.
Learning #3: 3/8″ feathers and wedges work well. 1″ feathers and wedges work well. I have no end of troubles with 3/4″ feathers and wedges – the wings of the feathers bend really easily, I’m not sure they split the rock here any better than 3/8″ wedges. I’m going to try some 1/2″ next week. I also might make a “punch” that sits over the top of a 3/4″ wedge head – so I can drive it cleanly.
Learning IV: We did some straight sledge/slab splitter work – split slabs without resorting to feathers & wedges. Really nice splits – hard work, but really clean, almost natural looking edges.
Learning cinque, AKA Angles on either side of spars, AKA ratio of side span to center span.
Behold, the humble and amazing suspension bridge:
There are three “spans” of the bridge: the center span and the two side spans. I’ve been pondering something for a while: why are either of the side spans usually half the length of the center span? Because of the cruddy available spots for a tripod, we found out the hard way.
By way of diagrams (generated with the truly friggin’ awesome Algodoo). Imagine a decent tripod setup, now imagine what happens as you scoot one of the tripods (towers, spars) away from the center, towards the anchorage:
Because of the available “flat” surfaces and anchor points, we ended up with a tripod very close to an anchorage – and I watched the rigging carefully as the line went up (I kinda knew it wasn’t going to work). The shorter the side span becomes, the more force is directed on the top of the tripod towards the center of the span.
I suppose one could anchor the back leg of the tripod – but that seems to me like that would introduce some exciting new forces into the system. Better to build the system so forces point straight down on the top of the tripod/spar…