retaining wall help please

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Annpan
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retaining wall help please

Post: #226092 Annpan
Mon Mar 14, 2011 10:23 am

We need to build a few retaining walls in our garden (which slopes towards our house)

I have been googling and watching youtube videos but I can't seem to find what I need.... (all seem to be for pre-cast blocks designed to build raised beds rather that a proper retaining wall)

We have heavy clay soil and a height of around 8 ft that needs to be retained, in 2 or 3 terraced steps preferably

We have lots of heavy breeze blocks around (I don't know what the term is for them but I believe them to be the right ones for the job)

So does anyone know about this kind of thing? what type of foundations do we need? and what height should they be? I know drainage is important, we'll make sure there is sufficient.

Can we build one 3 ft high, fill it, then go back 3ft and dig a found for the next one on top? :scratch:
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boboff
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Re: retaining wall help please

Post: #226097 boboff
Mon Mar 14, 2011 10:56 am

I am no expert at this but ideas would be

1. With the footings I would try and drive some spikes into the soil, get down at least 3ft if you can, then put concrete base in to cover the tops of the spikes, 18 inches of concrete as a minimum I would suggest.

2. On this concrete base build your walls using the breeze blocks laid on there flat edge so the thickness is at least 6 inches, shove in some grey down pipe every few blocks so they are at ground level at the front of the wall for drainage, use 10mm chippings at the back of the wall around the other end of the pipes so aid drainage.

Doing it this way I think you could get away with one wall, I would look at "buttresses" every 6ft if it's quite a long wall, but you could also turn the blocks so its flat and also longest across the width of the wall, then on the next level you turn it 90 degrees and end up with a two block deep wall, the staggering of the joints is very important.

If you just want the 3ft rise, then I would go for 12 inch footing and just keep the blocks flat and the wall 6 inch wide, this will cope admirably I think.

Hopefully
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Re: retaining wall help please

Post: #226120 Thomzo
Mon Mar 14, 2011 1:40 pm

Sorry Boboff, but with a heavy clay soil, I would recommend a double thickness wall as the weight of wet clay can put a huge pressure on a wall.

Ann, I'm not a builder but when I had some retaining walls built last year my builder insisted on a double wall; concrete blocks at the back and faced with brick with a very small gap in between. Even then, one wall has already cracked. If you have a very long wall, consider putting in rubber joints every so often so that the sections of wall can move independantly of each other. That way they are less prone to cracking.

How are you going to walk and down? And, just as importantly, how are you going to get the lawn mower, push chair etc up and down? Steps are easier for walking but make sure you have a nice wide slope somewhere for machinery etc. Think of the worst that could happen. If one of you ended up in a wheelchair, how would you get around the garden? You wouldn't want to have to move or re-landscape if that happened.

Drainage is important but where will the water go? Does your garden slope down away from the house? Then perhaps a pond at the lowest point would be a nice way to cope with runoff. My garden sloped down towards the house and the previous owners hadn't made any provision for the water to run away. As a result my garage flooded regularly and I would end up paddling across the patio. So when I put the retaining walls in, I allowed for a soak away at the bottom of the wall, a gravel area, slightly lower than the main patio, that will hold the water temporarily. It works a treat.

Which way does the garden slope? If it slopes down to the north the retaining walls will shade out plants on the downside. If so, consider having more, shallower terraces, so the plants at the bottom of the walls will have their tops in sunshine. If the garden slopes down to the south a couple of nice high terraces will give you some great south facing walls to grow fruit against.

I have one of those 'Garden Expert' books about garden structures. It gives some great advice for depths of foundations, widths of walls, materials and techniques. I would imagine you could get one from the library.

Have fun designing your new garden.

Zoe
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Re: retaining wall help please

Post: #226121 boboff
Mon Mar 14, 2011 1:46 pm

All good questions.

My understanding of these things is limited, but I think the footings and the "pins" are what it is important to get right, and without them your wall will crack.

Anyway, advice blind is never a clever thing.
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Re: retaining wall help please

Post: #226129 darkbrowneggs
Mon Mar 14, 2011 2:33 pm

Might be worth googling Gabion Cages This is a quick linky

But there are loads of places to get them, and you presumably wont need specialist building type knowledge

I haven't used them myself, but thought they looked good

All the best
Sue

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Re: retaining wall help please

Post: #226132 grahamhobbs
Mon Mar 14, 2011 2:52 pm

Annpan wrote:...........Can we build one 3 ft high, fill it, then go back 3ft and dig a found for the next one on top? :scratch:


This is an extremely steep slope, I would be very careful in what you are doing. 3' is probably over the limit for a simple 8" or 9" brick or block retaining wall. If it was brick I would do it in 13.5" wide brickwork. I would also add some reinforcement, something like BrickTor in every other course.

Clay moves a lot, it can rise and fall 2" between summer and winter. Unfortunately it doesn't necessarily do this uniformly and that is why you get settlement and cracking in so many old buildings. The only real way to avoid this is to construct foundations going down 1 meter, anything less could mean the wall cracking (although the BrickTor will help).

As I say I would be very careful doing this and it would be best to get some local expert advice from a structural engineer before diving in.

Just seen suggestion to use gabions. This is something we have done in a similar situation and is a good solution, in that the gabion suppliers will design the structure. They are easy to construct, in terms of making the cages and filling with stone, but you will have to excavate a large amount of soil.

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Re: retaining wall help please

Post: #226138 Annpan
Mon Mar 14, 2011 3:58 pm

Thanks for all the replies.

Zoe, our house is terraced and the garden is the same width as the house and slopes towards the house. the slope faces E / NEish with the garden shading it too.

The ground near the house has been extensively excavated and currently is all between 1 and 2 ft below finished ground level... and permanently full of water cause the drainage isn't in yet. heres a pic http://www.flickr.com/photos/snowdropsa ... 526612866/

We are looking to make the best of a bad situation frankly. There is a single 4 inch drain that goes under the house and ALL the water has to go through it.... we are putting in drainage and raising the ground level this weekend.

the gabions look like they might be the best option actually - though I don't like the look of them, they look like we can grow stuff up them to hide it.
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Re: retaining wall help please

Post: #226139 Annpan
Mon Mar 14, 2011 4:04 pm

just had another look at the picture, I think the height might only be 6 ft or so...
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Re: retaining wall help please

Post: #226149 grahamhobbs
Mon Mar 14, 2011 6:22 pm

The photo maybe deceptive but it doesn't look that steep. The more you can make the steps smaller and further apart the better, both structurally and visually. Measure the rise accurately and the distance over which the steps can go. 2ft high retaining walls can easily be achieved with blocks laid flat. They can also be cut, so you don't need to lay them in straight lines but can do them in gentle curves, with perhaps the walls widening apart where you walk up (and any the steps go), so leading you up and into your garden at the top..

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Re: retaining wall help please

Post: #226150 Annpan
Mon Mar 14, 2011 6:52 pm

Thanks Graham.... you might be right, I'm not sure how steep it really is because, until yesterday, we didn't even know what the ground level at the house was going to be. I'm hoping once we start back filling the hole we'll be able to see how it is all going to come together.

I'm grateful for everyones help on this.... sometimes my list of problems is just so huge I can't even begin to deal with it.
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Re: retaining wall help please

Post: #226153 TheGoodEarth
Mon Mar 14, 2011 7:31 pm

Gabions are ideal for this job.
No matter how much you push the envelope, it'll still be stationery

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Re: retaining wall help please

Post: #226156 Thomzo
Mon Mar 14, 2011 8:32 pm

Hi Ann

Your slope is a lot steeper than mine but the effect is the same. Don't worry, it can be sorted out with a bit of planning. Like you, I only have one small drain that takes all the rain water run off from the house and garden as well as being the main sewer for the house so in heavy rain it just couldn't cope.

I have a patio at the back of the house (the lowest point). I got my builder to slope it very gently away from the house (it meant digging out extra soil but it was worth it). At the base of the retaining wall is a gravel area on top of the clay soil. This is one brick below the level of the patio. The photos on my blog might help to explain. When it rains, this gravel area fills up and effectively becoming a balancing pond. This then drains away slowly. It really does work by storing the water. I am planning to plant some bog garden plants there eventually. It'd be great for the LO as it'll attract lots of wildlife, frogs etc.

I'm sure you already have water butts on all your downpipes. If heavy rain is forecast, empty them out, that way they fill first, slowing the water down through the drain.

Cheers

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Re: retaining wall help please

Post: #226167 darkbrowneggs
Mon Mar 14, 2011 10:35 pm

You could try growing Perriwinkle it is evergreen quick growing and has pretty blue flowers, or presumably if you introduced a bit of soil then Arabis and Aubretia and all those type of wall clinging alpines would look great.

All the best
Sue

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Re: retaining wall help please

Post: #226180 boboff
Tue Mar 15, 2011 8:00 am

Hello.

Looking at the picture, why not just leave it for a bit? Move the earth to level at the back of the house and then stone the rest rake and grass / clover it. This should stop it looking muddy and nature will soon find it's own levels. I have really heavy clay here too, and I did allot of diggerin about 2 years ago, put in "walls of mud" about 6 or 7 ft high, and the fall down, and that was with them being completely submerged in a raging river Tamar a few times.

The blocks won't go off, stack them for Later Ron. Try a permaculture approach with the Banks and plant fruit trees, bushes, nut trees, Hazel Holly Hawthorn, or a willow screen at the bottom as they love a bit of damp, and keep the earth dry etc etc. I well planted bank will give and take allot better than Cement, plus you get to eat from it.

The bit I digegred in two years is fully self seeded with Bramble, Dock, Budlieagh, and those spikey palm reedy things, as well as Himalyan Balsam, Japaneese knot weed and some Hog Weed for good measure.
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Re: retaining wall help please

Post: #226181 Annpan
Tue Mar 15, 2011 8:23 am

yes we could make the slope a bit less steep but it really needs to be easily accessible for everyone.... I don't think we could just leave it as it is really...
As it stands LO needs carried up to the garden, she's 4 and we all need the freedom of her being able to go in and out under her own steam....

I had a chat with the OH about this and we think we *might* just have a 2 ft wall and then a slope.... we need to be able to use the ground not just for grass (growing our own food and plenty to sell, we follow permaculture principles and try to use as much as we can) So it seems to make sense to terrace it.

A screen or 2 of willow has always been part of the plan... to protect the house in the winter and soak up water running down the hill, they will get coppiced heavily in the spring to be used for fencing, baskets and firewood (that is my plan anyway) We can't really grow any permanent trees near the house because they would cast too much shadow, but I'll have a good think about some of those other plants mentioned above.


a mini soak-away sounds like a fab idea Zoe! I was thinking about a patio nearest the house (so it isn't just a permanent muddy hole) I might leave out a slab or 2 for small 'soak aways' too...


I will take measurements when we are working at the weekend and see if we can space small walls far apart.
I have loads to think of now :cheers: :cheers: :cheers:
Ann Pan

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