Concrete Block retaining wall
I'm got a slope in my front yard that I want to remove by putting in a four foot high retaining wall. I'm planning on building the wall out of concrete block and covering the face with a stone facade that matches the front on my home. The wall is going to be about 90 feet long, running from the end of my driveway across the front of the house. I'm going to put in a PVC drainage pipe behind the wall and fill it up with rock to help move the water away from the driveway and towards the side lawn.
My question is this. I know that I must put in a poured concrete foundation, but how thick should it be and how wide?