[Cob] cob and earthquakes

[Dognyard]

I just got a copy of Rammed Earth House by David Easton. I sat up until
1 AM looking through it, and it appears to have a great deal of
information on seismic issues at the back of the book. I didn't go
through it, because it's just not an issue in our area unless one wanted
to overbuild for the heck of it, and because I was more or less skimming
through. Since the author builds in California, there is obviously a lot
of engineering and study going into code-allowed earth buildings in
terms of the structural integrity of the building. Now I know that hand
formed walls wouldn't have the same strength as a rammed wall, and he is
building with rebar in the walls, etc., but he does mention that the
thicker or more massively built the wall is - whether you use cement or
lime stabilized soil, or just a "perfect" mix of 70 percent sand and 30
clay - or wether you use rebar in the walls - the more likely it is to
survive an earthquake intact.

He also illustrates the restoration of a small store (it had some
cracked walls, but everything was still solidly standing) that had
experienced at least one earthquake. I didn't read it all, but I think
it was built prior to the 1930's and would have been rammed by hand and
not a pneumatic tamper...and no rebar. So wall thickness, wall height
and the quality of the clay/sand mixture used must count for an awful
lot in terms how a building of sand and clay (and straw) would withstand
seismic activity.

I would think too that design considerations like well-placed buttresses
and well-built interior walls would also help ensure that a wall doesn't
come down in a direction you don't want it to (if it comes down at all).

Karen Clouston
Alberta