Building on clay

["charles.hazard@zzzzzzzzzz" <charles.hazard@zzzzzzzzzz>]

Hi Charlie,
Sorry... I can't respond through the list.  I'm not sure where you
live (or are constructing your retaining wall), but I can give you some
basics that will pretty much work anywhere.  I'm in New England USA,
and our winter frost can really toss stones around without all
precautions.  I am also uncertain as to your relative skill level of
dry building.  In many climates, clay, is a regular hell-raiser.  It's
sort of the wildcard of the foundation world, so you want to take
precautions.  Nevertheless, if you stick with your plan of building a
foundation depth of half the ultimate height of your wall, you should
be just fine.  The trick will be in putting together that foundation.
In the old days we would start our foundation anywhere from 1/4 to 1/2
in depth of the height depending on the soil composition, and in many
cases our foundation would simply be to start the wall below ground.
Around here there always seems to be plenty of field stones, and
byproduct stones, with which to build.

Although I still hand cut my stone with featherwedges/wedges and
shims/feathers and wedges and stone axes of different weights,  I do
use a couple modern short-cuts for foundations as well as some
components of the wall.  The old terminology for wall components is 1.
Face Stones, 2. Backers aka "Back em ups", 3. Ratlins (they rattle down
the inside of the wall and fill in the voids between larger stones), 4.
Chinkins/Chenkers (fairly small flakes of stone from cutting used to
wedge stones tight, and 5.  Coarse Sand.  Forgive the terms, but the
Mason from whom I learned is currently 98.  He had been an ice man
before he took-up masonry.

I generally have crushed stone or river-wash stone and course sand
delivered to the jobsite.  If you can get crushed stone half inch, or
the metric equivalent, do so.  This is generally what I would prefer
for this type of application.  I would use this material for "Ratlins"
as well.  Your wall sounds pretty big (1 meter x 25 meters...wow), so I
would use some equipment to make a trench for your foundation with
machinery.  Digging into clay even a foot in depth is hopefully a party
that you can avoid.  I would then simply pour, level, and tamp the half
inch crushed stone into the trench (in say 6 to 8 inch lifts) up to
about six inches below grade, and then start your wall.  You will want
some degree of compaction, but there really isn't a need to over-do-
it.  I hope this helps Charlie.. Would you do me a favor, and post this
to the list?  I would actually respond a whole lot more frequently if I
could still post to the list.

Craig Disbrow, MBA, JD.
Disbrow Consulting
603 523 4259 (Voice)