Big retaining wall!!

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Oldham
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A friend of mine asked me to look at the failing DIY "retaining" wall at the end of her garden - I think she thought I could do something "cheap and cheerful'.
On inspection it's a pretty massive structure with a patio on top, the visible wall is about 2.5m high, I'm not sure there is much in the way of foundations and I guess the wall is/was largely being held in place by the two side returns which have now cracked vertically about 2m back, the ground at the foot of the wall is just rubbish that's been piled up and below it the slope continues, terminating about 3m lower at the bottom of the valley where there is a culverted stream.

I imagine a new properly constructed retaining wall would be a major engineering project (and there's only pedestrian access from the front of the house). She doesn't have much money and suggested that she abandon the wall, let gravity take it's course and build a smaller retaining wall about 2m back (across where the returns have started to separate) because she is reluctant to loose all the area. This would be about 1.8m high, plus the foundations, obviously still a major undertaking but maybe more realistic.

The thing that confuses me slightly is what the wall is retaining, given that the 45 degree slope it is built off appears to be stable and self supporting, is it in fact just retaining the infill behind it and does this make it less of a retaining wall? For example if she cleared the wall and all the infill away (which is presumably what's pushing the wall over) and built a new wall further up the slope with nothing behind it and topped it with decking would it need to be a retaining wall or just a substantial 1.8m high wall? This then begs the question does she actually need a wall? It's quite common in this area to see decking on similarly steep slopes supported by 4-5m old telegraph poles concreted in the ground.

Any suggestions appreciated, I'm just trying to give her a few options as it is quite a large part of her garden to loose. Personally I think if if you looked at this today with nothing there, like the neighbour on the left, you'd immediately say "decking on stilts" not "massive masonry structure"!

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If you are going to build a new wall and lay new foundations, then it may as well be done in front of that wall.
 
If you are going to build a new wall and lay new foundations, then it may as well be done in front of that wall.

I suppose somebody could, but it wouldn't me me, I have a real fear of digging footings at the bottoms of wobbly walls, and while those raking shores might look good they're supported at the ends by a bit of box section set in about 6" of postcrete!
And the rate for the job, seeing as it's a "mate", is about five hundred quid and a bacon butty.
 
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Gabions is an idea, I think the big problem, if I understand correctly, is that the ground at the base of the wall isn't flat, it's a 45 degree slope. I'd have to dig out below the wall to get a flat base for the gabions -
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Which means for a 2m wide 200mm thick level foundation to sit the baskets on (according to an online calculator I found) I'd have to dig down at least 2m below the wall, effectively increasing the height of the wall to 4.5m (which means increasing the base width to nearly 3m) and so on. I'm sure this could all be finessed if designed properly but it's still a lot.

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Clever stuff that, we did a job years ago on a huge stone wall with a terrace of houses on top, they were putting in ground anchors and injecting grout behind the wall, we had to point up the wall to stop the grout leaking out. It's still standing 30 years later.

I'll see what I've got in threaded bar at the back of my garage!
 
i wouldn't dig down for gabions. looks reasonably level behind the wall, it goes up a bit in fact. i'd fill in that void with soil or hardcore then have gabions from that level base going up a couple of metres. doesn't need to reach the top of the existing wall.
 
The pile behind in front of the wall is compost, soil and rubbish she's collected from the neighbours over the years and thrown over in a silly attempt to stabilise it - it's just mush. If anything the original ground gets steeper, especially at the front corner, I'm pretty much stood in a big hole taking the photo.
 
Is it a parking space up there?
In which case it's worth investing in a proper job, if it adds value to the property.
 
Is it a parking space up there?
In which case it's worth investing in a proper job, if it adds value to the property.

No, just a crappy patio. I did wonder if it would affect the saleability but she'd actually sold the house recently and the buyers had a mortgage approved (buyers later withdrew due to covid), I'd have thought it would be a liability that would be flagged up but maybe they just had one of those drive by valuations.
 
I reckon Bernard's solution is the best one.

Could you not achieve something similar with a few trenches filled with rebar and concrete with rods through the wall and some straps?
 

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