-
I have seen less holding back more, but concrete posts and gravel boards are not a proper retaining wall, although they might hold (or not). If you want a permanent fix, I would go with 9" hollow blocks on a concrete foundation, with the voids in the blocks filled with wet concrete to form a solid concrete wall. I will try to calculate material costs tomorrow.
ColinTheBald-
I think it's going to depend on my level of ability. I'm fairly confident I could do the posts and boards myself. Never poured concrete or set a block wall like you describe. It would be good to know more about it. How do the blocks key into the concrete foundation? Or does the wet concrete you fill them with mean they just "stick"? It would be about 18' long by 2' tall, for reference (if that wasn't obvious from the screenshot).
stevo_com
If I concrete these posts down 2 feet below the height of the concrete then double stack the gravel boards, that will give me another two feet of height. I reckon that would be enough. Is this a terrible idea?