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I need to redo a wall in our garden. Our garden is on two levels, with the higher patio section being ~80cm higher than the lawn. Currently, these areas are separated by a retaining 'wall' of wooden fence posts which are driven into the ground. I believe these were placed when the house was built in ~2006. They're now almost all completely rotten and falling off. I don't know what else, if anything, is supporting the soil on the higher level. I suspect nothing, although deeper than 6" or so, the 'soil' is mostly a load of rubble and concrete chunks. There is black plastic sheeting between the fence posts and the soil behind, which I suppose has stopped some of the rot but the poles are rotten from the ground up.
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So, I could redo it with more fence posts. I'm guessing this is the easiest option but a) the posts are definitely not coming out in one piece and b) presumably they will only last another 12-13 years. Maybe that's fine. If so, how would you approach this job? Dig the lawn out a bit to clear some space to set the poles? Do a section at a time? Some of the poles are cemented in alongside the steps.
Option 2 is to build a wall, but that might be even more problematic with a constant weight of soil pressing against it? I think ideally a wall would have a long 'toe' underneath the soil to stop it from falling forward, but to do that will be a massive job and necessitate a lot of earth being moved.
I don't want to spend loads. I'm potentially happy doing the fence posts but I think a structural wall is beyond my skillset at the moment.
WWSTWD?
I'm no expert.
Maybe some metal cages filled with rubble then filled with plants if desired?
Or maybe some combination of post crete base and tanalised wood?
A quick and dirty way to stabilise that might be to use railway sleepers stacked.
First level down, pegged in with rebar stakes driven through the holes into the ground. Second level on top, rebar driven through again, and so forth. I wouldn't build it too high unless you are stepping it, but that could work. However, even if well treated, the sleepers will eventually rot.
as above, wire gabions are a good option - galfan coated wire is very durable and can get cages made up to suit your needs for reasonable cash
other options are timber or concrete crib walls.
as would I beams and sleepers
or build up in blocks, and than tie into ground behind using geogrids
The more 'solid' you make the more you need to manage drainage from behind the wall and depending on options probably need to excavate behind and replace
Quickest and easiest could be to bang another row of posts in-front of the current ones. The old ones can happily rot away over time behind.
I have a sleeper retaining wall using rebar etc to go into the ground but it's only about 40cm high. Not sure you'd want to go much higher than that using that method without some other support. (IANA structural engineer).
Edit: (as above - some stepping might be required)
I have seen sleepers on their ends, dug into the ground which looks pretty cool.
3 or 4 uprights in the ground.
Decking cladded across the front and one or two along the top to hide the old posts and create a little seat.
I loves decking I do.
I've used sleepers in a similar situation and like the result. They fit gently into a garden and are low-impact.
These (assuming the photo link works) were new oak sleepers when done about 3 years ago. They are 250mm x 150mm. I dug down so that the bottom sleeper is 50% below ground, levelled the ground, compacted it a bit (i.e. stamped on it) and laid 3" of large gravel so the wood isn't sat directly on wet soil. Once the first layer was in, the subsequent ones are super easy and going 3-4 sleepers higher would be easy. The sleepers are screwed together with 150mm timberlok sleeper screws (diagonally in and down from the back so hidden). I did consider drilling vertical holes through the bottom layer to hammer some rebar through and into the ground but decided the mass of the whole thing was enough to keep it stable (and it has proved so) but I would probably do this in your situation as you're retaining a patio rather than our flower beds. Before backfilling the soil, I put rocks up against the back of the sleepers to improve drainage. The sleepers are easy to cut with a chainsaw. I did two walls, each about 4m wide and 3 sleepers high, each took about 4 hours. I reckon they will outlast me.
Downside of sleepers; they are heavy and awkward. These were 2.6m long and 100kg+ each.
Lots of ideas here - and I can vouch for them as a supplier. I also used some of their reclaimed tropical hardwood sleepers to build some compost bins. These are hard as iron and a lot more rustic.