# Forum Home Renovation Retaining Walls  Retaining Wall - What size sleepers?

## Tubby2

Gday all,
I'm ready to start on my retaining wall and wanted to know what size sleepers I should be buying for the posts and whales.
The wall is 900mm high at the highest point and is retaining shale/clay. I've had the wall dug out for a couple of months and it's retaining itself atm. 
Any ideas? 
Cheers

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## Planned LScape

The sleepers are 200mm wide(they vary 5-10mm sometimes), I would go 2.4m lengths 75mm thick 
Just find your post heights, add them all up and get the extra few sleepers according to how many Lm the posts end up coming to.; You may be able to get 3m or 2.7m lengths for the posts so that it works closer to your cut length saving on wastage.

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## Terrian

for an easy wall, I agree with PS above, treated pine, but why go the easy way, get your self some bridge timbers, they look just fantastic and two STRONG people can just about move them  :Smilie:  
(will post pics one day)

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## Tubby2

So I should be using 200x75 sleepers for the posts as well as the wales? 
I was under the assumption that I should be putting these in about 800-900 deep using quick set and a bit of gravel under the posts. I have since been told by a landscaper that 500mm is more than enough and every other posts doesn't even need to be that deep.
Does this sound right or am I better off taking the extra time to go deeper?  
Cheers

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## Planned LScape

Whats the backfill material like...clay, sandy soil? 
500mm would prob be ok, 600mm to be sure. Make sure you put ag pipe behind and screenings to keep the weight off the wall also, often gets overlooked. If you took the extra time it cant do any harm, and gives more piece of mind

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## Geoff Dean

> I have since been told by a landscaper that 500mm is more than enough and every other posts doesn't even need to be that deep.
> Does this sound right or am I better off taking the extra time to go deeper?
> Cheers

  Do this at your own peril. 
I was given almost the same advice - 600mm deep for I beam and 2.4 x200 x 75 sleepers. Wall went from 500mm high to 1200mm high across a slope and was retaining a clay, soil mixture. 
Within 12 months I had to completely redo the wall as it had pushed over around 75-100mm at top and was going further. 
It is amazing how much good advice you can get after the fact, could get none before hand. 
I have since learned that you should have as much post in the ground as is out, so in the case of 1200mm high have 1200mm in ground as well. 
Initially had 450mm diameter holes, 2nd time around went to 600mm diameter and also placed another upright behind wall 1/2 way between each existing upright. 
Finally, I put another wall 600mm out from the existing wall and made it 400 lower. Same deal with all the posts. This is now where my raised bed vege garden is. 
Better to put the posts too far in the ground and use more concrete than necessary than not enough. It is far easier to do it the first time, not much fun when you have back filled to the wall. 
It took me a solid week with a pick and shovel to dig out behind wall, and it was not a fun job.  Next time I am going to build a rock wall. I reckon it will be easier. :Biggrin:

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## Terrian

> So I should be using 200x75 sleepers for the posts as well as the wales?
> I was under the assumption that I should be putting these in about 800-900 deep using quick set and a bit of gravel under the posts. I have since been told by a landscaper that 500mm is more than enough and every other posts doesn't even need to be that deep.
> Does this sound right or am I better off taking the extra time to go deeper?
> Cheers

  200mm x 75mm will be fine for the uprights, rule of thumb says whatever is out of the ground must also be in the ground.  
Person preference - wall anything more than 1 sleeper high should not have soil / clay backfill against it, basically what happens is the soil/clay gets wet, expands, drys, contracts, more soil / clay falls in to take up the space, more rain, more expansion, sooner or later the wall is going to push over. 
I generally dig 400mm x 400mm square holes for the posts, put in the post, at least 2/3 fill with concrete (not quickset, standard has a higher mpa rating, and is cheaper) leave for at least 24hrs before making use of them. 
The sleeper walls around here are backfilled with broken bricks, concrete, roof tiles,  pavers, rocks, hardly any soil / clay touching the walls (been a good way of getting rid of the paver imbedded concrete paths)

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## burraboy

I believe that treated pine suppliers have spec sheets available for sizes and depths of timber for retaining walls.  As a rule of thumb, same in ground as out of ground works well.  The tip for using porous backfill is also excellent.  You should also put an ag drain along the bottom of the wall at lowest ground level.  Build the wall with a lean initially to allow for settling over time.  It's water that pushes over walls, not soil.

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## Terrian

> I believe that treated pine suppliers have spec sheets available for sizes and depths of timber for retaining walls.  As a rule of thumb, same in ground as out of ground works well.  The tip for using porous backfill is also excellent.  You should also put an ag drain along the bottom of the wall at lowest ground level.  Build the wall with a lean initially to allow for settling over time.  It's water that pushes over walls, not soil.

  I have to disagre with you, clay type soils expand when wet, and thats what does the damage...

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## Canetoad

am i missing something here I can't see how high the wall is. Just be aware that a retaining wall over 1000 high needs an engineers tick.  I have seen a fair few walls pushed over in non clay soils so the water must be doing something, Go for over kill building a retaining wall is much more fun the first time than rebuilding it.  :Smilie:

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## Planned LScape

I did a job last year where the engineer called for 1.6m into the ground for 800mm above...I then had to order twice as much steel beams for the posts...and concrete 
But the site was on the fill side of a new house cut, right on a boundary

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## JulianH

Mitre 10 and Bunnings have plans for building retaining walls. 
I followed a combination of the deck plans on my deck, plus advice from forums...I plan to do the same on the retaining walls/garden beds. 
I'm going with Red Gum I think, not TP as I don't want to have to trouble with staining it.
Julian

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