Not can it be done, it looks beautiful. My DH did this - not only a DIY job, he had never worked with concrete before so it was all a "maybe this will work, let's try it" project! He says he set the outside stones carefully level (you will need to buy or borrow a 6' level, for something like this) on a packed sand foundation. Wet the sand; the slower concrete dries the stronger it is. He filled in the center with some rip-rap (we had some broken up concrete from past jobs), then poured over that, the usual quick-set concrete dry mix bought from HDepot, wet it down, and leveled it. Then let it dry for about a week, misting it down gently every day. Then he set the second course, filled in the center with concrete mix only, did the whole level/daily wetting. We live on a hill with slippery clay soil and a lot of continual settlement, and the stairs have been rock-solid perfect since 2003. HTH!

Hi Weedy, Thanks for the reply-- We currently don't even walk on the deck, the beams meeting at the outside-left corner have completely rotted away and not supported by the posts... I swear it's inertia and friction holding the thing up this point... I like your idea of having just two retaining walls and leveling out the area, the trouble is that the lowest spot in my yard is not quite as low as I'd like the area under the deck to be, meaning in order to water away from the house I'd have to either build a retaining wall there or build up a small mound to provide grade. This is why I was thinking of building retaining walls on 3 sides to box in the whole area under the deck while incorporating a set of steps into one of the walls (probably right side) to keep access. For the footings, I figured I needed to 4' lower then the lowest point around me, just wanted to hear another opinion... this a lot of digging!! Regarding posts and retaining walls... my idea was that the footprint of the deck is exactly the same as the retaining wall--so are you suggesting making the deck larger then the footprint of the retaining wall, meaning the posts are set "outside" of the retaining wall? or smaller? I wasn't really expecting to gain much by incorporating posts into the retaining wall, just trying to maximize my space under the deck for storage. Currently the deck is about even w/ the window on the right side, and off by only a couple of feet on the other, so expanding the deck parallel w/ the house could only grow by 2-3' before it starts to overhang the windows (I think it's 8' now, so it could grow to maybe 10')... I could certainly grow the deck perpendicular to the house, that might be the best option, that would also allow me have more of the deck in the sun which would be nice. I'm doing a a "hybrid DIY" on the build, I'll be hiring a family friend who is a professional carpenter, so I do have hourly costs associated with the build, but all the same I'd still rather spend more now to get a better build :) Ideally I'll be getting "serious" around July 1st, applying for the permits, taking down the old deck, etc...

I believe you with the measurements. It's just that it doesn't show up well in the photo so is misleading until you clarify twice :-) And I understand how you're going to remove more from where the grade is higher toward the corner of the wall. And all of your drainage from behind wall sounds great. "Yes" to having swale above wall to direct water from spilling over it. (But I know in real life that some may go over the top of wall.) Nevertheless, the design should be directing water to run toward ends of wall since you want it to go around the sides of house. This would happen both above and below the wall. We haven't seen the slope so don't know what you're working with (against?). Keep in mind that you DON'T want water rushing down the hill, collecting directly at the back of the wall, and then running left or right to get to the wall ends. Such a volume of water, running fast, would wash out material from the back of the wall. Chances are good that you don't have a lot of room for creating a swale. You might need a flume instead. Keep in mind your wall should turn 90* back into the slope at its ends. This part of what it takes is to prevent washing out from behind the wall. There are a lot of details for this project and site that we are unaware of, so ask where things are not clear.

CMUs (what you're calling cinderblocks) need to be built on a concrete footing, mortared together, tied to the footer with rebar, and the cells filled with concrete. Is this what you're looking to do? If so, I've found that the 8x8x16 CMUs from Lowes are ~$0.40/ea cheaper than my contractor yard. Occasionally you can find someone on craigslist clearing some out for a buck apiece, but it'll take you a while to get what you need. Or are you referring to the interlocking concrete wall blocks, that go on a gravel footer and lock together with pins or a lip? If that's the case I wouldn't even consider the ones from the big box stores as they're trash. You want to buy those from a paver and stone supplier.