I am planning build two successive retaining walls 2' high (4' from bottom of footer to top of the wall), and approximately 38' long. The horizontal distance between the two walls will be approximately three feet, with a step of 2' from the top of the bottom wall to the top of the top wall, thus forming a small 3' planting terrace in between. The total drop from top to bottom will be 4'.
I live in Southern California, so there is no frost line or threat of freezing. The soil at 2' feet below grade is a composite of hard clay/ virgin rotted sandstone. Both walls will be holding back a flat grade. The newly formed terrace was previously a rounded/sloped mass of unsupported earth, which was luckily only 4' high. The area above the top wall runs flat to the back of the lot. Permitting is only required for walls that are greater than 4' in height in my area.
My plan was to dig down to 2' below grade for each wall and pour a concrete footer that is 8" in depth and 2' wide. I was planning on using standard 8x8x16 cinder blocks for the wall itself. Based on this, roughly two courses of cinder block would be below ground, while another three would be above (yielding an exposed height of 2' for each wall).
I am going to use rebar to tie the retaining wall to the footer, as well as to provide lateral support through bond beam block running the length of the wall. I will also fill and cap all blocks with solid concrete. Both walls will be water proofed, be back filled with gravel (covered with filter fabric to prevent clogging) and have a sloped perforated drainage pipe leading water away from the wall.
The reason I have decided to build in this manner, rather than using a pre-cast concrete dry stacking system, is that I plan, for aesthetic reasons, to face the above ground sections of both walls with flagstone veneer.
I have a few questions about this setup.
1. Do you think the placement of the top wall in proximity the bottom wall would present any structural issues? If so, should I reduce the size and depth of the footer in the top wall, thus reducing overall weight? 2. Do I have to worry about moisture with regard to the underground courses of cinderblock? If so, should I raise the footer? 3. Given that I am building a French drain, would I even need any weep holes in the wall?
I am trying to build the most stable structure possible, but am worried that I might be going into overkill mode. Any suggestions on my questions above, or better way to build a similar type wall while still allowing me to face with flagstone veneer would be very much appreciated.