Retaining wall

[i_am_fubar]

Question for you chaps. I have a 1m drop in my garden that I want to split with a retaining wall. my soil is heavy clay.

I've read that I should have a 1/4 thickness of height. so 250mm. Would using 215mm hollow concete blocks suffice, filled with concrete and rebar down each 'tube'?

Naturally, this will include a 430mm by 150mm concrete foundation (with the rebar embedded in it).

I also have provisions for a butress half way along the wall (total length about 4 meters) going into the high side.

I'm also aware of the requirements of weep holes, drainage...etc and will plan them in. My main question is whether that thickness and style of wall will suffice?

Also, I saw on a website, some stainless steel brackets you embed into mortar when laying bricks to give you a perfect thickness of all courses. Does anyone know where you can buy these?

Cheers,
Sam.

 

[i_am_fubar]

Now with pictures

Here is the garden:

Untitled

• i_am_fubar
• 27 Feb 2010
• 1

(note the bricks to the right as the start position of the wall)

And here is the wall I want to build:

Untitled

• i_am_fubar
• 27 Feb 2010
• 1

The additional truss on the back of the wall will be tied in with re-bar, however, the bricks will not mesh.

As stated above, the voids are to be filled with concrete and rebar.

Slight adjustment to height, it's 0.9 of a meter.

So, think it'll be strong enough? I would like to think so :/

 

[Chukka63]

sounds a bit overkill to me.
if you want to use those blocks thats fine.i would put a bar every 450mm(to suit block runs)embedded in the foundation as you mention.theres no need for the pier on the back of the wall.then fill with concrete.

 

[i_am_fubar]

Cheers for that. I have always been one to over engineer. Maybe I should just make a bomb shelter while I'm at it :/

But yea, that knocks a few blocks off the cost. Ummm, next question... Is 150mm deep enough for the foundations? I plan on laying rebar in them to make reincofced concrete, but are there any other options?

Finally, damp proofing and drainage. I've no problem with the agrigate and drainage channel. But how does the damp proofing work? I get the looping a waterproof membrain from the top of the wall to below the drainage pipe. But surely the foundations will wick water up (a problem as I want to paint or render the wall) in the same way a missing damp course does. But putting a DPC in would make a weak point in the wall. Can anyone explain the proper/best way of doing this?

Regards,
Sam.

 

[i_am_fubar]

have read the http://www.pavingexpert.com/featur03.htm site about retaining walls. As I thought, it does make mention of a DPC in the wall. While This won't affect the vertical load bearing capabilities of a wall. Would it not be a weak point against lateral forces?

In addition to this, how would one put rebar through it without jeopardizing integrity?

 

[r896neo]

I certainly wouldn't put a dpc in a retaining wall but you should put a run of dpm over the rear surface of the wall or it will be constantly wet. Obviously you must not do this if you are not draining behind the wall, but you should be doing that anyway so....

 

[i_am_fubar]

was planning on using a standard slab foundation DPC, the type that comes in a bit sheet. As to the drainage, I'll be using some solvent weld 40mm drain pipe (not bothering to glue it) with an array of holes drilled in it. Then surround in gravel (all behind the DPC) to assist drainage. End will empty into a soak away.

 

[r896neo]

You'd be better off trying to get your hands on some land drain perforated pipe but that of course is only if you have somewhere to drain it to??

 

[i_am_fubar]

I have unearthed an old drain cover under the god-knows-how-old patio. I was considering draining it into there. Or, down the side ally that leads to the road.

 

[r896neo]

The pukka job would be wall, dpm perforated 4inch land drain pipe with a generous surrounding of clean stone backfilled in oder to try and get a continous line of stone up the wall. Then drain the pipe to wherever you chose, preferably soakaway or local water course.

To be honest on a wall your height and length though if its not easy to drain the pipe away you could forget about it, have plenty of clean stone, plenty of low level weep holes and that would probably be enough. I'd advise the first method but if you are going for the simpler method then you need to make sure it all doesn't get bunged up with silt and i would throw a geotextile membrane between your stones and backfill.

 

[i_am_fubar]

I was planning on putting a permeable membrane between the loose stone and backfill. Else the clay will just soak into it in time.

I'm pretty much ready to go then, trees are down, and I have space for the bulk bags of aggregate (although B&Q trade depot is out of cement grrr).

I guess most questions will now be moved into the building section for concrete/mortar/foundation queries.

Cheers guys. Will try and put some pictures in.

 

[Deluks]

Clay? Trees down?? Might get some swell. I'd be putting some compressible polystyrene board in behind it all too. Probably overkill, but I'm like you.

 

[i_am_fubar]

I don't plan on doing anything with the area above the wall for a good few months. So there should be plenty of time for the soil to settle. Even the back filling will take a month or so to be complete.

 

[Deluks]

So when the summer approaches it will dry out, but come winter again?

 

[i_am_fubar]

Hmmm. Good point. Is there anything I can actually do about that though? Surely the ground level will just go up and down. I would like to think the wall will be strong enough to withstand the forces of expanding clay.