building a wooden retaining wall - foundation depth??

[DavidST2]

Evening all,

I'm intending to build a 1.25 m tall retaining wall in my back garden using lengths of treated wood.

I'm trying to achieve something similar as is shown at the following link: http://www.rd.com/content/openContent.do?contentId=18205

The wall will approx 4 m long and I intend to use 4" post (4 of - placed 1 m apart).

The question I have is how far should the post be sunk into the ground to provide a good foundation to work with? Is there a simple rule of thumb?

All help would be appreciatted! I'd rather not have to re-build in a few months time because I have understimated anything?

Thanks in advance

 

[Deluks]

Depends on what it's holding back. For a really strong retaining wall, concrete in rsj's with sleepers slotted in the webs, but that might be overkill in this situation. You'll probably get away with somethingx2 timber, (treated joists)

For posts use 6ft long, 2ft of which should be concreted in. Advisable to put a layer of large gravel behind the wall, followed by some landscaping fabric to keep soil from clogging up the gravel, which will act as drainage and prevent damp earth from sitting against the timber.

 

[DavidST2]

Thanks for the reply.

Yeah - slight overkill with the RSJ's - but it did cross my mind as well. I have gone at least 2 (probably more like 3) feet deep, concreted them in and have tied it with a few timbers (treated) that are below ground. Overkill again probably...

thanks!!