If I were splitting wood on the ground, this would be a different story. Actually, the little 16" ax is not an especially good splitter ax. The head is too narrow. And most of my usage has been roughly at waist or torso level. Your pre-chainsaw ax example makes a lot more sense to me now.
I used a Maddox/madd-ax all my life, it is not a shovel, not a hoe or an ax, but it can do the job they do in skilled hands.
It is best for breaking up that first layer of red clay, under the four foot of sand you have already removed.
When an large animal died on the farm, we dug a 6' X 6' X 6' deep hole so the wild animals & plow would not unearth the animal.
I never knew why 6 foot cube was the right formula, I was just glad it was not an eight foot cube.
Lucky you, I am guessing if I dug down 3 feet I might hit solid rock.