HOW IS ARCHY FORMED?

June 24, 2008 11:17 PM

How was this made?

Slightly different angle here.

I discovered this while fucking off into the woods for a while today. Based on its location I would assume it to be made by random idle kids/drunks/stoners or some combination of the above three. On the other hand, I am near a large university and it's possible this was built by an expert civil engineer stoner kid.

I understand the theoretical aspects of why an arch stays up, yet based on the ad hoc nature of this one I don't immediately see how it was built or see it as likely that someone constructed a special scaffolding to build this on a concrete drainage pipe. (Though this is not implausible.) The readily available materials are rocks provided for drainage, as seen, as well as possibly wood presumably gathered from being in the woods.

Note in the pictures the fact that small rocks and rock chips are liberally used as shims between the large rocks.

Is there simply some neat simple trick behind this that I don't know? Is it just easier than it looks?

posted by TheOnlyCoolTim to technology (15 comments total)

Rock balancing.
posted by amyms at 11:27 PM on June 24, 2008 [1 favorite]

P.S. There are lots of pictures and how-to videos about rock balancing (also called rock stacking) if you google around. The arch formations are rarer than the vertical stacking.
posted by amyms at 11:28 PM on June 24, 2008

I notice there is a pile of larger rocks in the lower right of your pictures that almost looks as though it had been stacked. My bet is that those rocks were used to support the arch before the keystone went in.
posted by i_am_joe's_spleen at 11:30 PM on June 24, 2008

I'd guess that the pile of flat stones at the bottom right of those pictures were used as an impromptu scaffolding to provide rough support for the main part of the arch (see also chips on the bottoms of the stones in the arch).
posted by theclaw at 11:32 PM on June 24, 2008

The rocks in the bottom right didn't strike me as stacked while I was there (especially as visible in the second picture they looked consistent with rocks being dumped there by the crew making the drainage), but, interestingly enough, when I took these pictures, the next (of four) drainage pipes I was standing on did have three decent-sized rocks stacked on top of each other. They didn't seem sufficient to explain the construction of the arch and obviously wouldn't necessarily be on the next pipe over as part of the arch construction, but could be part of this.
posted by TheOnlyCoolTim at 11:45 PM on June 24, 2008

but could be part of this.

I mean that they were obviously stacked but the stacking didn't necessarily seem requisite for the arch.
posted by TheOnlyCoolTim at 11:49 PM on June 24, 2008

There's a landscaper in my area that makes those. I'm not sure how he does it though.

Try asking a landscaper or a stonemason.
posted by C17H19NO3 at 11:59 PM on June 24, 2008

I once built a structure somewhat like that one by getting two semicircular bits of wood, placing them on the ground, building the arch over the top, then removing the bits of wood once the structure was ready to support itself.

Whether this would work with rough stones, I'm not sure.
posted by Mike1024 at 12:44 AM on June 25, 2008

Carefully.

For more examples, look up Andy Goldsworthy
posted by The Esteemed Doctor Bunsen Honeydew at 1:14 AM on June 25, 2008 [1 favorite]

When arches are built from bricks or cut stone, there is usually a temporary wooden former underneath on which the stones are placed, starting at the sides and working inwards to the middle. Only when the arch is complete can the former be removed.

I would guess that in this case a former of some sort was used. Perhaps the person who built it has one that they use for every arch they construct, or perhaps they rigged up something temporary from found materials. The first seems more likely, as it would be difficult to construct a former from twigs and rocks.
posted by le morte de bea arthur at 2:39 AM on June 25, 2008

This guide to making dry stone arches explains that they must have a former in place before the keystone is dropped in, and suggests a bent piece of plywood as a likely candidate.
posted by roofus at 2:47 AM on June 25, 2008

Andy Goldsworthy, who was linked above, makes a whole range of natural sculptures like this. I read a book of his once and he described the method for making a rock arch. In the beginning stages, he uses other rocks as support for the arch. Apparently it took him several tries before the arch stood when the support was removed.
posted by twirlypen at 6:16 AM on June 25, 2008

I'm from St. Louis. At our science center there is a family/kids activity that uses foam blocks to teach kids how the St. Louis arch was constructed. You build up both legs evenly on both sides and as they begind to lean inward, you place a keystone in the center so the legs come together and support one another. Most arches seem to be the same principle. Here is a completely random video of the activity im talking about.
posted by jmchrist at 7:05 AM on June 25, 2008

It seems Google's version of Geocities cut me off for the time being. Lower resolution pictures here and here.
posted by TheOnlyCoolTim at 10:49 AM on June 25, 2008

Either formed over something that was then removed, or someone had a lot of helpers to hold everything in place while it was being built.

That´s how you party like a rock stacker.
posted by yohko at 2:21 PM on June 25, 2008