Jerry - OHIO wrote in :

If the water just goes under the slab it might wash out the soil.I had
my 150 Truck fall through the floor.Builder didn't use wire and half
the pour was only three inches and never hooked up drain,pea gravel
settled two foot because they poured on frozen ground.I now have a
new condo cause part of the kitchen flour dropped three inches.
Jerry

http://community.webtv.net/awoodbutc...oodWorkingPage

Hence the "if you have soil that drains" in the part you snipped. That
would be a very important consideration.

I always assumed that my garage drain was hooked up to some plumbing.
After a couple of weeks of daily snow, the drain backed up. I used my
hose to wash out the "pipe", to no avail. After it finally drained on
its own, I stuck my hand down and found sand. Lots of sand. I later dug
some holes in my back yard and discovered that 10 inches of topsoil
covers a prehistoric sand dune.

--
Steve Bell
New Life Home Improvement
Arlington, TX