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How to build gabion walls on sandy slope?

Hiya

I'm looking at placing gabion walls down the side of my garden, along the top of a slope down to a gull.y

The ground is a very poor combination of sand and fill pebbles which erode with a dirty look, so the walls will need to be bedded thoroughly.

Cages are 4500x300x600 (LxWxH)

The current plan is to build a trench 1.5 times the width (450), tamp down blue steel, pour concrete and reinforce with mesh, then place gabions.

Questions:

How thick should the reinforced concrete be?

Should the gabions be anchored with star pickets or similar through the concrete slab?

Is this overkill, or is this going to be a disaster?

Thanks!

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Comments

Dave-1

Good Afternoon @BodgeJobsRUs

🙂 Gabions will work but I think your sizing may need to be adjusted. Love gabions, they allow drainage, dont generally need foundations and last for years.

You mention that your cages you want are 4500x300x600 (LxWxH)

As a rule that I have used when building them the base of a cage should be approximnatly 2/3rds the height of the cage for them to retain soil, If you are looking for a fence style thing where the cage is not holding back weight then you can go narrower. but still keep in mind the overall weight and likelyness of it to topple if pushed.

Here are some of my gabion walls I have built

Freestanding gabion walls For holding nothing, just looking great.

Gabion Wall to stop water ingress to garage (this is the tallest one and also the narrowest. mainly the soil is solid up to about the 1/2way mark then fill above)

Front corner gabion wall To show how I stepped the gabions on a sloped surface. This is part of what i would do with your question.

Wiggly pavers for sloped path in front yard Shows how you can build a gabion on a slope, this is still going strong.

Large gabion retaining wall Shows the 2/3rd rule. No foundation was used. The small section I had dig through before I installed the walls for the stormater pipe I compacted but still in the 3ish years since that corner of the cage has sunk maybe 3cm.

Foundation wise, as long as the base you are laying the cage on is compacted I dont think you need a concrete footing, if you are worried about the soil underneath the cage being undercut then a foundation would also be undercut.

If you are building on a slope, consider terracing the area. A second run of cages midway to also help keep the soil from moving.

You are holding back your concrete driveway plus any cars sitting on it. Thats a resonable hefty weight. The cage I have built to hold back around that weight is 800mm by 900mm high. Gabion retaing wall and gabion steps It needs to hold the soil plus 3T of water in the spa. A small car is 1.2T plus your concrete so a larger cage I would suggest.

How far down have you dug with your sandy soil? It may be worthwhile digging a test hole to see what is there. The starposts is a good idea tho really I wouldnt think necasary as the weight is what gives the cage its strength, a post driven deeper will still have all that weight piviting on the upper part if it wants to roll and wont stop it.

Have a troll through my bookmarks 🙂 Very happy to answer any questions as they are perfect for free drainage and stability.

Dave

BodgeJobsRUs

https://www.workshop.bunnings.com.au/discussion/comment/53530#Comment_53530

Hi Dave!

Thanks for the detailed answer. Gabions are great, aren't they? I built a gabion garden bed the other day and have caught the bug.

I was concerned about the thickness thanks, so I'll recalculate.

The drive is part of a ROC for the neighbours and is pretty well constructed (apart from the lack of drainage = erosion = gabion walls). However none of the walls will abut the drive as I'm planning to have a "pathway" alongside the drive for drainage and access. Does that alleviate the issue of pressure from the (infrequently used) drive?

From my measurement diagram three of the horizontal lengths are where I am intending to terrace, but that's a very big job - prob need a bobcat for the terracing. 24m is enough for now!

Max height I can go to is 600, which will very nicely tidy up the slope.

Under the misery that is the sand and fill I'm pretty sure it's sandstone, so if I can skip the star pickets that'd be great.

Hope that makes things a bit clearer?

EricL

https://www.workshop.bunnings.com.au/discussion/comment/88977#Comment_88977

Hello @BodgeJobsRUs

I totally agree with @Dave-1 in regards to not putting in a concrete base but instead digging down and terracing the foundation for a much more solid base. I believe the digging part is the only hindrance that will be slowing you down. Let's hope the sand and pebbles are not too deep. Would it be possible for you to draw a sketch of the gabion walls and where you'll be positioning them. Will you be placing a second row to act as a retaining wall?

This is an excellent project, and I don't want to add more complications to it, but have you had a thought about drainage, storm water flow along with soil erosion. I propose drawing it on paper first and speaking to a landscaper who is knowledgeable about water drains and soil reinforcement techniques in heavy rain.

If you have any other questions we can help with, please let us know.

Eric

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/110254#Comment_110254

Good Morning @BodgeJobsRUs

I like @EricL 's suggestion of drawing us a sketch, top down and also side profile with some measurements on it as I am a little unsure what you mean by

"The drive is part of a ROC for the neighbours and is pretty well constructed (apart from the lack of drainage = erosion = gabion walls). However none of the walls will abut the drive as I'm planning to have a "pathway" alongside the drive for drainage and access. Does that alleviate the issue of pressure from the (infrequently used) drive?" The part I am unsure of is the path along the driveway? There dosnt seem to be a lot of space for that so think I have missunderstood something.

Sandy soil = Shovel.
Dig out the width to the depth you want with a shovel and see how easy/hard it is with that sandy soil. I would not dig imediantly next to the concrete driveway at least until you are ready for a cage the same day as if it is sitting on sand it may pour out weaking under the slab. It may be an idea to do it in sections as you work your way only the route. You dont want cave in's due to stability. Plus you will also need somewhere to store the excess soil.

Thats a nice Gabion and well down on the rounded edges! 🙂 Did you put ties between the sides? and yeah I think gabions are brilliant with so many types of usefulness. One day I actually want to build a wall with hardwood offcuts in a gabion. I think it would look pretty nice. The cage I would sit on pavers for that instance tho 🙂

Dave

BodgeJobsRUs

https://www.workshop.bunnings.com.au/discussion/comment/122491#Comment_122491

Morning @Dave-1 and @EricL .

I'm sorry I don't have a top down view, but I cobbled this together (red = gabion walls, blue = drainage under gravel path approx 70cm wide).

A major issue which caused the erosion is run off from the drive. As my neighbour is not going to fix it, I need to sort this out. I'm not going to build a wall next to the drive, as I might need access in future. I also am not planning to put drainage behind the wall, as that space gets horribly dry, and the gabions will allow good drainage as needed. Oh- landscapers fabric will be attached to the garden bed sides to help hold the dirt in!

This photo is from my digging yesterday:

Terracing is 3.6m (top), middle 5.4, bottom 4.4. I'm planning to use more decorative walls with some space built in for trailing plants which is 30x50cm WxH (using this for inspiration)

Long RW is 9m from top to angle, then ~14m from angle to bottom. I have changed the plan so that wall will be 50x50cm WxH.

I hope that covers the plan? My back hurts...

Yep the garden bed has ties at two points along the sides and one point at the apex of the curve. I also lined it with some smaller mesh and used smaller stones behind the visible ones as I read they reduce bowing by spreading the pressure out more evenly. I'm glad you like it! I've got another one to finish.

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/130392#Comment_130392

Afternoon @BodgeJobsRUs

That second photo you just posted gave me perspective when i double clicked it lol It went from a narrow area betwen driveways to a much larger area 🙂 You shouldnt need a midway retaining wall. or a base retaining wall unless you want to terrace the whole area one day. 🙂

02 20-06-2025.jpg

Blue thin dual lines high side of the driveway is the copperlog retaining wall.

Driveway

Green edged area is the gravel path 700mm wide

Pink rectanglar sections are gabion cages.

The dotted lines are at the distances you have suggested for the markings?

As I was sketching out the top down view I was thinking of drainage and how to deal with it. If you dig a sloped V styled trench along the edge of the driveway and place in the bottom a 100mm socked agi pipe Reln Stretch Ag-Pipe 100mm x 8m Slotted and Socked and then Kink it out under the gabion wall and part way down the slope (note you will need to have something to stop erosion on the outfall) Then back fill with 8mm gravelso the pipe is at least 80mm below the surface that would take care of the drainage, doin it in multiple sections alongthe driveway so if one part clogs up it wont be so bad and the volume of water can be mitigated.

The 50 by 50 gabion gace sounds good, For a straight same level run when joining them skip on of the middle basket panels and stitch the outside and 1 middle panel together with the same screw. It makes for a tidier straight line.

Examples below.

01 20-12-2023.jpg

02 20-12-2023.jpg

For the steeper section I would suggest to step the baskets so they have roughly the same amount above the ground as the level run of the baskets.

I would do the baskets first and then the gravel path, installing the agi pipe under the cage for the sections as you go.

Dave

BodgeJobsRUs

https://www.workshop.bunnings.com.au/discussion/comment/135294#Comment_135294

Hi again @Dave-1

Just to confirm, these are the measurements:

The long wall will be at the top of the slope down the gully, well away from the drive. That's why I was making sure I had the right idea of securing it so it didn't fall!. But dig, level, angle a little into hillside? and don't back fill too high sounds reasonable.

Good idea about the drainage, will install when I get to the cross walls. Though I've got the ag pipe for the drainage along the drive ready to go.

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/138570#Comment_138570

Afternoon @BodgeJobsRUs

🙂 lol I had them a bit out then hahahahah

Still plenty of space to only need one wall 700mm away from your driveway 🙂

I would go for level cages over having any angle on the actual cage. It would make life a LOT harder to build and keep straight plus would look a little odd. The 500 by 500 filled with stone/concrete/bricks would be enough.

With the drainage from the agi pipe I would actually go as far to make up a little rock stream with a rubberised sheet underneath the rocks, no concrete with a dish shape type deal. Start from the bottom and work your way up making sure there isnt too much weight for a slip/cascade effect. It would look good in the rain 🙂

Dave

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