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Retaining walls and gabions.....
DIY Si - 1/12/12 at 05:30 PM

Afternoon all.

Following on from my roofing question, I have another about retaining walls.

The garage in question will be cut back into the garden so it'll need a retaining wall to stop the garden washing it away. Most of the wall won't be visible once the garage is built, so it's looks aren't too important. The more important thing is its construction and it's cost.

Basically, I want this done for as little as possible. I think the three most viable options are brick, block or gabion.

Brick is pretty but expensive. Therefore not much use for me.

Block is cheap for materials, but given that it's a retaining wall I'd be best off paying someone to build it. So labour isn't cheap, but cheap materials may offset this. Not sure how to work out how much block and what not I will need for the wall, so I'm unsure how much this may cost.

Gabions are about £350-400 or so for the gabions, plus what ever stone I fill them with. I can find a few places that are £20 or so a ton, and the internet seems to think I will need about 20t of stone, so about another £400. Labour is free, as even I can stack stones in a line.

Anyone got any preference on which way to go? With the upcoming weather I am tempted to go the gabion route, as it can be sub-zero and not matter. It will also save me on ground works and footings. But it is really as easy as it seems?

LoMoss - 1/12/12 at 05:59 PM

How about a rammed earth embankment. All you need is a geotextile and drainage aggregate and a whacker plate or jumping jack.

Easy as


HTH

Moss

owelly - 1/12/12 at 06:07 PM

If you have room, use gabions. To go proper locost, get some galv cages off IBC tanks and fill them with rocks. If you can't get the cages, just use the IBC tanks, cut the tops off and use them.

LoMoss - 1/12/12 at 06:07 PM

What I have done is us rebar mesh as the face and hooked it back into the earth with rebar. You can fix this to scraps of mesh.

Its a bit like a soil gabion.

You can plant into the face or grow grass on it to stabilise the face.

example

Moss

JoelP - 1/12/12 at 08:15 PM

Myself id be tempted to build it with blocks, sheet it and then backfill with gravel. This might be an awful idea though, who knows? Blocks are dirt cheap and the wall goes up fast and easy.

DIY Si - 1/12/12 at 09:27 PM

Perhaps I should fill in some more details. The garden the wall needs to hold back is roughly 1.25/1.5M high, which is supposedly the max height of simple walls, and slopes upwards from there. It's also 70ft long and made of a fairly clay-ey soil. I have no idea what difference if any that makes. Also, the wall will be U shaped to fit round the back of the garage, and one side will be hard up against the neighbours garden, which is slightly higher again.

Whilst I agree there are several locost ways of doing this, the Mrs will want it to be vaguely proper. And I don't really want it knocking my shiny new workshop over either! I suppose I could have a bit of a stepper slope behind the retaining wall up to the garden, so that would lower the height needed, but not too much, as there are plans to put a green house on the ground behind/above the wall. For that reason, I don't think a rammed earth embankment would work, due to the embankment part of it. The rebar mesh bit has merit though.

v8kid - 1/12/12 at 09:45 PM

I've just done this and in Scotland you need a building warrant which covers the English party wall agreement . Drainage and granular backfill was a big cost and if you are in surburbia you will need interceptor traps.
I used blocks and tanked the structure.

1.2 m is not really a retaining wall but if it is a party wall you have a duty to your neighbour to make it safe and are liable for any consequential damages. That's why I did it right do you want to risk it with loopy half baked ideas of ibc's cut in half

Cheers!

DIY Si - 1/12/12 at 10:13 PM

V8kid,

I suspected that the gravel drainage stuff would be a large part of the cost. One of my main worries is the potential depth of the wall. The thicker it has to be, the less space I will have to build the garage as the Mrs will only allow me so much of the garden for this. The wall with the neighbour is the primary concern as I can't risk screwing that up. My garden is my own fault, but I don't want to pull his garage down as well!

Ivan - 2/12/12 at 03:34 PM

quote:
Originally posted by LoMoss
How about a rammed earth embankment. All you need is a geotextile and drainage aggregate and a whacker plate or jumping jack.

Easy as


HTH

Moss


Way back when (1975 or so) I designed a couple of 2,5 m high reinforced earth retaining wall using a geo textile (Bidim) in Simon's Town - they have survived successfully since then with no sign of settlement or movement when last I looked (yesterday) as one supports the parking at the library.

The main thing with them is that the fill must be properly compacted and the fabric kept taut so you need to support it with shuttering when compacting. Also Bidim was the only available geotextile at the time but is far from the most suitable, use something that can develope and mainain tension without creep.

Also you need to protect the exposed face from UV degradation or animal or other damage by cladding it.

I was quiet proud of the walls at the time as they were amongst the first to be designed in Cape Town, unfortunately I have lost my design calcs and can't remember how I did it. I later set up a spreadsheet to do the job but have lost that as well.