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when stone walls tear
Thursday, December 19 2024
I'd noticed recently when looking at the older, more southerly stone wall, the one I now call the Chamomile Stone Wall, that parts of the wall have slowly begun to "tear." Tearing, as we know, is when a material weakens and fails when subject to tension. In this case, the tension appears to be the movement of the wall perpendicular to its plane, mostly caused by higher material moving horizontally more than lower material. This is th result of the fact that the bottom of the wall is better anchored to the ground, whereas the top is relatively thin and subject to more lateral forces from things like the wind or the levered effects of ground movement. The tearing manifests as widening vertical gaps between individual stones as the wall bows and widens slightly in the direction of movement. In the two worst places where this is happening, the wall is clearly leaning somewhat towards the direction of movement. Since a wall like this depends entirely on the compressive force of gravity and friction between stones for its integrity, there isn't much leaning it can do before gravity forces a collapse. I've counteracted this movement in the past by building towering buttresses that lean against the wall to counter the movement, and this works very well; a bent wall can withstand enormous horizontal forces applied to its convex side.
Today I wanted to fix the two places where wall tear seemed to be the most severe, though I only ended up fixing one. I started at a bad spot near the wall's middle where the wall was leaning so much that I fear an imminent collapse. (Mind you, this wall has largely stood the way it is for five years since I constructed it, and movement in that time has been minimal. But the wall is very thin and doesn't take much of a lean before it will collpase.) Initially the plan was to build a flying buttress by stacking a column of stone a foot or more from the wall in the direction of movement and then gradually lean that stack against some point high on the wall. But as I worked, the wall (which was uphill from me and about five feet tall) seemed threatening. If it decided to give out while I was there, it could kill me. So I worked cautiously, paying close attention to the wall so I could jump out of the way if I heard or saw something happening. I actually did hear some rock movement when I put down the first heavy rock of the new buttress, suggesting that it moved the ground enough to cause movement in the wall generally. That wasn't good. But I kept working, stacking the buttress and beginning the process of connecting it to the wall with long narrow rocks that I used as beams. But something about where I connected to the wall triggered something bad and the wall started to collapsed. I jumped clear of it all seconds before several hundred pounds of rock, mostly small stones, sprayed out in a fan. Their collsions with each other were so energetic that the rocks were immediately covered with white scratches and the air smelled like gunpowder.
This collapse was not a bad thing, because it allowed me to completely re-engineer that part of the wall. I left the rock on the south side of the wall as it was but ripped away all the rock on the collapsed north side all the way down to the ground. I then built a bowing wall up to a height of about three feet, enclosing a void about ten gallons in size. I then used large sleet-like rocks to form a roof over this void. That provided a new wide base for a much stronger wall that had the added benefit of providing shelter and storage space for numerous small creatures. To get the wall up to its former height, I hiked up the steep escarpment just to the west of the wall and found a number of large beam-like rectangular rocks. The result didn't look dramatically different from how it had looked before, though now it concealed a void. As you know, I love building such voids, and now it was clear that including them can be a way to strengthen a wall.
Meawhile Gretchen had gone with our friends Cathy & Roy down to New Paltz to eat boutique limited-edition sandwiches at Lagusta's chocolate place in New Paltz (she is that village's most famous vegan entrepreneur). The particular sandwich initially sounded great to me, so I'd wanted Gretchen to get me one while she was down there. But by today the sandwich had changed to one featuring beets, one of the few vegetables I don't much like. But I had such confidence in Lagusta that I told Gretchen to get me one of those sandwiches anyway. So when I got back from all the stone work, there was a beautiful sandwich waiting for me. I ate it with an open mind, not dwelling too much on what exactly was in it. It was absolutely amazing, and I wouldn't've wanted it to taste any different from what it tasted like. Helping it somewhat was the fact that the beets were golden beets, which are a bit less beetlike. My only quibble was how oily that sandwich was. (I had to use a lot of soap to clean my hands afterwards.)
This evening I did some work with my ESP8266 Remote system in preparation for adding INA219 I2C voltage measuring boards to certain installations. This will allow me to better monitor 12v batteries and perhaps even implement systems to automatically prolong the life of the battery in some scenarios. The plan is to include voltage measurement as just another default thing that can be measured, along with the existing weather data. I also decided to include latitude, longitude, and elevation for devices that might be mobile. Since the data being collected is no longer explicitly weather-related, I changed the name of the table where this data is logged from "weather_data" to "device_log."
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