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How deep? - retaining wall construction
gregs - 17/1/15 at 07:50 AM

Hi all

In the spring i'm going to be putting in a number of retaining walls to 'stage' parts of my garden - these will range from 50cm step to 1m.

I'm planning on doing this with galvanised I beams with sleepers slotted in between. Question is, how much do i need to bury of the post. I'm sure the 'rule of thumb' was 1/3 of the post under the ground, but maybe that's for free standing fences....

So my thinking is - a post that needs to stand 1m above ground - 1.5m long, 50cm under ground. A post that needs to stand 50cm above ground, 1m long, 50cm under ground (more than the 1/3 rule but makes sense in my head).

If anybody has any experience on this or expertise, then guidance would be appreciated before i order the beams and get them dipped....

Thanks,

Greg

snapper - 17/1/15 at 09:48 AM

My retaining wall has 30cm footings with the same of brick below dirt level then 3 course of brick above
It's a cavity wall brick front concrete block rear with a French drain a perforated pipe behind running to a surface drain in the corner of the patio which then runs to the rain water drain corner of the house.
I did have a patio that flooded until the water ran around the house
I don't now

Smokey mow - 17/1/15 at 10:54 AM

What is the subsoil you're putting the posts in? Is it cohesive or non-cohesive? And how large (width not depth) are you planning to make the holes that you put the post in?

In basic terms the more you put underground in both width and depth, the lesser the chance there is of it moving over time.

gregs - 17/1/15 at 01:36 PM

quote:
Originally posted by Smokey mow
What is the subsoil you're putting the posts in? Is it cohesive or non-cohesive? And how large (width not depth) are you planning to make the holes that you put the post in?

In basic terms the more you put underground in both width and depth, the lesser the chance there is of it moving over time.


It's heavy clay - was hoping to keep holes as tidy as possible and only concrete if I have to...

coozer - 17/1/15 at 02:11 PM

All depends on the ground, water table and all sorts of other factors..

My initial thought was to lean it back a bit, fill the triangular bit behind with gravel on a breathable sheet and allow some kind of runoff and drainage if theres any water behind.

Good luck,
Steve