We want to improve the soil in the front yard, to give it more depth and less rock. But we cannot get too close to the roots of the big trees in the front. So for the large Spanish Oak, we are going to put in a retaining wall allowing us to bring in more soil for it's roots. The retaining wall basically replaces the existing wall between the yard and the front bed (which runs along the front of the house from the door to the corner of the house).
The idea is that this wall starts near the front door about 3 courses of stone high -- some 18 inches -- and then decreases as it runs across the yard until it meets the wall on the edge of the property (that we just put in) at just 4 inches above ground level.
But, of course, that means it runs right thru the trench near the corner of the house. And all that has been dug out. So we need to put back a new wall support underneath what will be the ground level.
We could do a solid wall, as we have elsewhere, but in this case, we do not want to impede the flow of water thru the ground to the French Drain, which is just on the other side of the new wall. We begin with a lower level of large cinder blocks. These are 16 inches tall by 8 inches deep and 8 inches wide. 5 of them at $1.68 each from Home Depot.
We space them out and put a layer of thinner concrete blocks (only 4 inches tall but 16 inches wide) on top, to form most of a surface that we can put a concrete base on, and then 6x6 limestone blocks. It appears we can put two rows, or courses, of 6x6 limestone blocks to get even with the property line wall. The bottom course will be underground, and probably a portion of the top one, when we eventually fill things back in with dirt.
Once we have these cinder blocks embedded in/on concrete and mortar, we can bury it all.