Retaining wall on top of concrete AND next to fence

Question

I have an outdoor area which is currently pebbled and retained next to a fence. I plan on removing the pebbles and turfing, and am also considering planting a green hedge because I don't like the look of the fence. The problem is the current retaining wallhas a large gap AND is on an incline ( at the junction of the front and back of the property). To complicate things, the floor of the gap is cement. I'd like to close that gap to allow for my plans above, with the possibility of creating a small retained garden bed against the fence for my potential hedge. I think the pictures will do a better job of explaining the situation

I think the "easiest" solution is to just fill the gap with soil and turf over it, but I feel as though the moisture of the soil against the fence will accelerate rot, and I have some mild worry about the soil pushing against the fence. I'd prefer to build something that will prevent these 2 problems, and I think a retaining wall is the right solution, but am unsure. The issues with building a retaining are that (1) the bottom of the gap is concrete (which makes putting posts in for a retaining wall complicated I think), (2) the gap is narrow on the front end, and (3) there is a significant incline which makes putting in a level retaining wall more difficult.

I'd be grateful for any advice/recommendations.. Thanks!

Answer 1

Fill with dirt will be a fail. Yes, that will rot and push out the fence, so don't.

Concrete block wall would be the way to do this, with the bottom blocks cut and mortared to get it level on the slope, and drilling holes to grout in rebar to attach it to the concrete below. Since you won't be looking at it with the fence there (and it's pretty short) I'd just use plain mortared concrete block, not fancy free-stack landscape blocks that will be harder to cut.

Working-space wise, you're going to have to dig out and pile to the left to make room to work, then move stuff back when the wall is done. You can keep your stone pilled separately and use it for a drainage layer on the bottom (be sure to put in weep holes at the bottom of the wall for drainage as needed.)

Answer 2

Don't put earth touching timber, it won't last long.

Anyway, how about filling that gap with the pebbles you already have. That would not rot the wood, and would probably look nice. And cost nothing ;-)

Yes, the pebbles you have are a bit small. I have a similar gap between house and garden all the way around (this is central Europe, we have weather) and it is filled with large pebbles, 8 - 20 cm.

People solve the problem of pebbles obeying gravity by inserting flat stones (even old roof tiles) or sheet metal, vertical along the sides or in the middle of a slope, to keep them in place. Wood will not do. No matter what it's treated with, if it gets wet regularly it won't last a decade.