How to repair lifted concrete retaining wall?

Question

Hi, I need some advice on how to repair this garden retaining edge.

Some of the soil has washed away, and the concrete garden edging has lifted and become loose. There are also some natural rocks underneath that have moved.

I’d like to make it stable again and stop the soil from washing out in the future.

What materials do I need? Would concrete be enough, or do I also need crushed rock or drainage material?

MitchellMc · Answer

Hi @vicky17,

Thanks for uploading the additional photos. They make it much easier to see what's going on.

I think your theory about the Bird of Paradise is quite plausible. Its root system was likely helping to bind the soil together, and once it was removed, the soil would have become more susceptible to washing away during heavy rain.

Before anything else, I'd lift the loose concrete edging and any displaced rocks, remove any loose soil, then add and compact some crushed rock to create a firm base. This will help support the edging and reduce the chance of it settling again. You can then add concrete and place the stones from the front back into position. Once done, add a bed approximately 30mm thick on top of the wall and bed the edging back down into it, locking it in place.

You don't need to encase everything in concrete. Use just enough to stabilise the edging. After the concrete has cured, backfill behind the edging with well-compacted soil.

If you continue to notice water washing through this area, it would also be worth considering improving the drainage behind the edging, as preventing the soil from washing out again will be just as important as repairing the existing damage.

Mitchell

vicky17 · Answer

Hi Mitchell,

Thanks so much for your advice.

I’ve already bought a bag of Concrete Set from Bunnings, but I’m not really sure how to use it correctly for this repair.

I’ve attached a few more photos from different angles, as you suggested.

I think this may have happened because we removed a large Bird of Paradise plant that was growing right next to this area. My guess is that its roots were helping to hold the soil together, and once it was removed, the soil became loose and eventually washed away.

I’d really appreciate any advice on the best way to repair it using the Concrete Set, or if there’s anything else I should do before using it.

Thanks again!

MitchellMc · Answer

Welcome to the Bunnings Workshop community @vicky17. It's wonderful to have you join us and many thanks for your question on repairing a wall.

It's a little difficult to tell exactly how this retaining edge is constructed, or the best way to repair it, from a single photo. Would you be able to upload a few more images from different angles and perhaps one taken further back so we can see the whole garden bed and how the edging ties into the surrounding area? That will help our members provide more specific advice.

From what I can see, it appears that the soil has washed out from behind the concrete edging, allowing it and some of the supporting rocks to move.

If the edging has been in place for quite some time and this is the first significant movement you've noticed, with no major damage to the surrounding structure, then there's a good chance it can simply be repaired rather than replaced. Repositioning the rocks and concrete edging and securing them with concrete could be a suitable solution.

However, before doing that, it would also be worth considering why the soil has washed away in the first place. Improving drainage behind the edging, adding compacted crushed rock as a stable base if needed, and backfilling with well-compacted soil can all help prevent future movement. Depending on how much water flows through this area, a small drainage channel or agricultural pipe may also be beneficial.

Once we can see a few more photos, our members will be able to provide much more targeted advice on the best repair method.

Please let me know if you have any questions.

Mitchell