Retaining wall advice

[i_am_fubar]

Hey there,

I've got a garden on a slope, and I've been digging it out into 2 level steps. The difference is about 700mm between the layers and the soil is heavy clay with a lot of stones in it.

There is also a conifer stump that the walls runs next to (Roots removed, getting stump out will be heavy work though).

I want a Mediterranean look, and was thinking a rendered wall painted white. Though I have heard a lot of stories of render falling off retaining walls. poured concrete would be an option but I am trying to save costs and use up the mountain of rubble I have.

My idea was to build a wall such as follows:



Where I build a front man made board (MMB, such as MDF or hardboard) wall. Then build a rubble wall behind it, filling the gap between the MMB and rubble wall with concrete as I go. I figure it would give the strength and appearance of a rendered wall, but without the risk of the render falling off.

My questions, are basically:

What is the viability of such a design?
What level of back drainage would I need (considering I want to grow a fig tree behind it)?
Considering that no length of wall will be greater than 3000mm without a corner, what level of pinning would I need to do?

Cheers guys,
Sam.[/img]

 

[noseall]

Without sounding patronising i would not give a wall like that a single hope.

Any retaining wall needs to be sturdy. You are better off building a 9" solid block wall then decorating it with rubble and render.

I know Thermo disagrees, but i would not use timber in the construction of a retaining wall.

 

[Thermo]

totally agree with you on the design noseall, the only timber retaining walls we build are out of sleepers and if they are a certain height they are mesh reinforced an backfilled behind with concrete. ive seen many built out of masonry that are a waste of time and money. a properly constructed sleeper one will last as long if not longer in some case!
Me landscaper you builder!

 

[noseall]

Me landscaper you builder!

You learn fast Grasshopper.

 

[i_am_fubar]

May not have made it clear, but the timber would be taken away after the concrete has set.

You say it won't last, but I've seen walls made of mortared rocks before, and they have held back some rather large embankments. Is there a specific design principle they employ?

Also, by 'rubble' I mean mis-matched bricks, chunks of paving slabs, large rocks (dry stone wall size)... etc, not small chunks of masonry.

I guess I could swap out the 'rubble' for concrete blocks. But would it still be viable to use the half brick wall/half poured wall to get the smooth face?

If not, how can I render a retaining wall in such a way that it doesn't come loose?

Cheers,
Sam.

 

[noseall]

If you are serious about using shuttered concrete then you need to design some shuttering that is going to hold back some darn serious push.

When that concrete goes in, 4"x 2"s as you have designed won't stand a chance. Besides which they would interfere with the footing concrete.

What you would need to do is lay a concrete foundation with rebar sticking out of it. This footing needs to be poured and allowed to set.

Then design a very sturdy shutter to hold back the concrete whilst it knits with the rebar and footing. This should be done after the footing has set.

Like i said, you are best building a conventional wall.


You are right to say however that some walls fare better than others. I have seen dry stone walls stand up to a lot of punishment, but we are talking about clay.

 

[Thermo]

what you have to remember is the walls youve seen made of "rubble" are either dry stone walls, or they may well have been simply faced with the "rubble" and are a lot thicker behind

 

[r896neo]

If you build a normal 13-9 inch wall, which i think you should, then simply put a large taped dpm behind it and then your render will be fine, if you use this method you need to do a real proper job with drainage behind it though!

 

[i_am_fubar]

Ok, revised plans.

For the cost of sleepers, I want to go down the block and render route. The most suitable blocks I've found are these http://www.wickes.co.uk/Dense-Concrete-Blocks/invt/154028. Though I'm sure there are better, like the ones with voids in them for filling with crete. Does anyone have a link or cost for an easy supplier for these types?

I would build the wall with the blocks flat (so that each row is 100mm, and the wall is 215mm think). Then putting in a moisture barrier and drainage holes at the bottom. Back fill with gravel and top with earth.

As a revision, the wall will now be 900mm high with a patio on top. The longest straight stretch of wall is 3600mm.

Is this a stable enough design?
What additional support would be needed on that style of wall?
Any pillars/tie points?
Is the standard damp membrane you can buy for putting under concrete floors the type I should be after?

Cheers

 

[i_am_fubar]

Pictures clear up the description:

(not to scale)

As I'm keen to hide the weep holes. The drainage section will be the bottom row of blocks where I will drill holes through them. This will be buried under the level of the patio.

A trench of loose gravel will be just in front of the wall all the way round, terminating at a downward slope (Thus channelling the water away).

Also, I assume a DPC can't and shouldn't be used in a retaining wall due to the lateral forces? If so, will that not create a route water could take to destroy render?

Wall width = 215mm
Wall height = 900mm

Any comments, criticisms, thoughts?