Sandbags for slope stabilistion

[AnthonyL]

The upper part of the back garden is quite steep and during one of the storms early last year a whole heap of shrubbery, earth slipped down and over the retaining wall. A couple of trees were dislodged also.

There is a lot to clear up and I'm wondering about putting the dislodge earth into sandbags and putting on top of and then behind the retaining wall. This has the advantage of finding somewhere to put a ton (guessing) of clay type soil, helping to stabilise against further soil erosion and maybe helping to provide a platform to climb up and maybe seed some suitable ground cover.

I guess I don't actually want it "flood proof" as I'd not want rain build up behind.

So do you think the plan is workable? And what of the many varieties of sandbag would be most suitable? It'll hopefully be there for a while.

Any other tips?

[Tricky Dicky]

You might be better off using Gabions filled with stone. You do not need the enormous type you often see on motorways there are a variety of sizes. Just the facing side needs to be aesthetically arranged and the back filled ideally with limestone chips although any old rubble will do. They will let water through so no drainage problems and if you leave pockets of soil you can even get a few creepers to take hold.

Richard

[AnthonyL]

Thanks, looks a good shout and am tempted to mix and match with sandbags. I'll have a closer look.

[Andrew]

Send us a photo of the damage. Structural retaining walls needing to hold back a considerable amount of wet soil need careful thought.

[Chris Hogg]

Sandbags get to look awfully tatty in a fairly short time. I'd go with gab ions of the appropriate size, filled with a mix of soil and stones, and plant rock-plants into the exposed faces.

[Tim Lamb]

In message [e-mail]>, AnthonyL [e-mail] writes

Hard to find a cheap woven plastic claiming UV protection.

Those big bags used for bulk deliveries last about 18 months in the Sun:-(

>

[AnthonyL]

[Andrew]

That's a very steep slope !

From what I can see the wall does not seem particularly well made or substantial. I wonder what sort of foundations and rebar reinforcement it has ?.

A slope that steep is probably stabilised by roots. Proceed with caution before you remove too much.

[Robert]

Used prefilled fabric bags to stabilise/build a retaining wall for a raised lawn on a National Trust property. Probably about 5ft high. Then applied grass seed. Has worked well and looks good . Was a great deal of work moving the bags though, which included a short boat trip !

[nightjar]

On 08/03/2021 14:42, Tim Lamb wrote: ....

At a previous house, the sandbags supplied to us for flood protection lasted about six months.

[Chris Hogg]

That's a steep slope. I'm not sure how you're going to position gabions or sandbags on it to hold it back.

But another approach would be to use a cover of deep-rooted plants to anchor and stabilise the soil. Vinca, Lamium maculatum (Dead Nettle) and especially Crown Vetch come to mind. A description of Crown Vetch and its use, here

(OK, so it's an American description, but it works just as well over here!) Get seeds here

[AnthonyL]

Indeed. It is basically rock with some clay/top soil. I haven't tried to see if I can make any impression on it for maybe using staples of some sort. I guess that ivy had spread all over and some of it turned into shrubs and trees.

I'm not sure how you deduce that. The retaining wall has retained what was behind it, it just couldn't stop what came over the top.

Oh I'm not touching the vegetation that is above the retaining wall. But some of it has slid down which is what caused the damage to the shed. A couple of ivy trees, an Ash I think, and a Hawthorne that is now leaning against an adjacent tree. That might need a tree surgeon as it is a bit big. It's slid down about 2m.

[AnthonyL]

Thanks Chris. The underlying surface is rock. I think there is now an area just up from the retaining wall that looks like a bit of a hollow and I might look at putting something substantial there so I can build up a bit of soil behind. I'm not sure deep-rooted is going to work as there is nowhere for deep roots to go, which is why the vegetation that has tumbled down didn't hold on to its position.

[AnthonyL]

It's not a part of the garden that is ever going to be seen. Though rock plants etc would help with re-establishing some vegetation. Ideally I'd like something that would inhibit the ivy from spreading. Ivy is everywhere across the properties on that bank right to the top.

[AnthonyL]

I certainly would not want to use pre-filled but using the clay/soil that has cascaded down in a way that it will be held would be great.

Do you know anything about the fabric bags you used?

I don't need a boat but a helicopter would be jolly useful.

[Robert]

Sorry cant remember but the following links might provide some info on this approach. The pre-seeding rings a bell. A great deal of labour was involved in my project due to the multiple handling involved in getting them on site.

I am sure there are others as well.

[AnthonyL]

This photo gives an idea of how much loose soil has eroded and slid over the retaining wall. I've got no ready way of getting up there even if I wanted to cut the shrub down.

[Andy Burns]

Abseil from the bus-stop?

[Tim Lamb]

No ladder available?

A search on slope retention gets any amount of civil engineering hits but little affordable/installable by a householder.

I know this is d-i-y but no interest from your house insurers?

You need a rot proof grid which can be pegged securely to the slope, trapping sliding soil but allowing plants to grow anchoring the surface.

18# agricultural Rabbit netting might serve to create in situ gabions. (roll out some netting, lay on some suitable stone to the lower half and then fold the top down and secure).

Throw on some soil to encourage plants and do another row higher up.....

[AnthonyL]

There is a convenient lamp post. Some of my neighbours have been forced by the council to put up fences to stop yobbos from hurting themselves in the event they climbed over the top.

My boundary is so thick with Hawthorn and Ivy that you can't get through so I escaped that expense.