I used to excavate each "raised bed" 12" deep and then assure drainage from that depth to some nearby lower spot. Then I amended that removed soil, and then cart it back to the site of the bed and return the new soil. Now it is raised above grade.
Now I consider the CLAY to be the "amendment", and I only want 20% to 30% of the new soil to be clay. Thus what I dig out should have 2 to 4 times as much "other stuff" added. In other words, sigh, store-bought "soil". That was not my original goal! I wanted to MAKE fertile soil from clay plus scrounged materials.
Next time I make a new bed, I won't excavate DOWN much more than I need to create a consistent slope towards my "drain-away trench". I'll go over to making raised beds that are ALL raised, and not sunken. Over time, leaching compost and worms will soften and then aerate the deeper clay layers.
>> I sit on a100' deep layer of clay.
I guess you won;'t be digging many French Drains!
>> It is either like quick-sand or concrete. Nothing in between.
You might laugh, but I took to heart the "rule" about never working soil while it was wet. So when I excavated my clay, I had to use a pick to break up the clay first. Yes, chip it out like a sculptor with marble.
Eventually someone asked me why I didn't soften the clay first with a little water, like overnight?
The answer would be "Because I was very very dumb!" or, at least, inexperienced.
You CAN make clay so wet that it sticks to your shovel and weighs even more than it used to. But even a LITTLE water makes hard clay soft enough that you don't need a pick. Or at least each swing of the pick breaks up more than just one little chip!
