Friday, January 4, 2013

Shaken Not Stirred


Many people make bucket lists this time of year. My listing bucket includes taking time to read more. 

This week  I have been reading a wonderful new booklet by Sean Adcock entitled 'Stonework'. He does a thorough job of analyzing and explaining some of the structural aspects of bad dry stone walling.

Whilst I agree with almost everything he says about proper walling methods and why walls fall down, I do question a concept of his, in the section on grading where he looks at the logic of placing larger stones below smaller ones in a wall. The sentence I am wondering about is ... "Generally a big stone on top of a layer of two smaller stones is vulnerable and unstable compared to a layer of two small stones sitting on top of a big or over sized stone."

Consider however:

Listing the bucket to one side, and then vigorously shaking its contents of small random size stones will eventually cause the larger stones to all come to the top. It is evident that the stones in the bucket have now found a more settled, more stable state.




Stone arrangement before being 'shaken'


After shaking - the stones are fitted better and are less able to be 'stirred' .

I suggest that the same thing may well apply to certain random coursed walls. Smaller stones in the wall will naturally continue to find ways to slip down between,( hence get lower than) the bigger ones below them.
Therefore large stones might often be better bedded in a wall on a selection of a smaller stones to begin with, rather than having the smaller stones (especially if they are much smaller) placed above them, complying with the natural selection of sizes per height exhibited in the previous 'bucket of stones' example.

Thoughts?

8 comments:

  1. It was always seen as a baaaad thing to perch big on top of small. When a big stone decides it wants to play elsewhere it will move easier when there is a pile of minions below it, small enough to respond to his whims and fancies and be bullied out of the way. Nick A

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  2. Yes but doesn't the structural principle of Galloway dyke (for just one example) contradict that theory?

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  3. The bucket thing works well for panning for gold but not panning for structure! I'll give you two examples. Two years ago I was fishing copes out of Lake Ontario and forgot one I'd set on a large boulder at the shoreline...despite the nasty storms since then, it's still there. On the other hand, if I'd put the boulder on top of the cope, the cope would be 4' under the sand by now. Two, I can carry my kid on my back much longer than she can carry me. You could argue that a wall would have more kids to support me, but those mosh pit crowd-surfing moments that happen at raves or Nuit Blanche only last until the crystal meth wears off! But, through stones are often bigger than the stones underneath them and yet they provide strength rather than liability, so keep stirring the pot... open and creative discussion is the best way to build!

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  4. The shoreline thing just proves that the small cope stone would still be there under the larger boulder - settled lower but more stable. If it was on top it would have been washed away. Thanks John for your input.

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  5. Intriguing thoughts John. Perhaps more of an aesthetic rule turned structural rule. We've all seen very large cope stones of various shapes solidly bedded onto much smaller stones below (and also large through stones structurally employed atop smaller stones). Another of the endlessly fascinating aspects of the craft. Hopefully a future PhD in dry-stone-wallology will prepare a more substantial thesis on the topic.

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  6. Believe it or not Dan, during my last trip to Scotland, Norman and I were interviewed by a lady who is actually doing a PhD on dry stone walls. I don't know if she'll be tackling some of these more mysterious elements however.

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  7. Forgive a novice for interjecting but is 'size' and 'gravity' not being a tad overblown in this debate - when dynamics are key?
    You saw the feidin walls with their seemingly random, zig-zag, crazy (or 'alive') structure which support bigger stones aloft.
    Indeed the whole wall is consolidated by the weight of large above small - that is - the dynamis of the arrangment. Not desined to be shaken except by sideways winds, still the principle is the same.

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  8. Good point. To be fair though, I suspect Sean was talking about horizontally laid stones in a wall. (Random laid, all the way through to coursed styles of walling ) However, should size of stones decrease in proportion to height of a wall? Like you, I'm still asking that question.

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