Sleepers come in standard lengths up to 3 meters. In this case most of the sleepers were 2.4 meters long. They were also 100mm thick. These are heavy duty normally used for walls higher than 1 meter. Less than that height, 80mm can be used or even 50mm if less than 0.4 meters high.

This was Hallett Cove, South Australia. I don't remember anymore who the builder was but he did mention that he wasn't able to build much beyond 900mm high without an engineering design.

I learned from my Dad, building tensioned barbed wire fence that soil is fluid in most cases. These posts would be holding back a lot of pressure from damp clay-based soil with little rock. In this neighborhood there are quite a few other retaining walls that were moving and a couple near collapse. I opted to place the posts very deep in a large diameter hole, they will still move over time but not much. Not too evident is that the wall and posts are leaning back into the bank by about three degrees which helps direct soil pressure down rather than against the sleepers. One meter between posts should mean that the holes don't need to be as deep, unless the wall exceeds 900mm. One end of this wall was 1200mm and as the sleepers exceeded 2000mm, that end post was 1500mm deep. Drainage behind the wall is important for the reason you've stated but I think it also reduces how much moisture is retained behind the wall, making the soil less fluid and with less weight.

@@madebyjnd I planned to make the posts as deep from the bottom of the wall as the wall itself will rise above it, plus an extra 30cm or a foot of concrete beneath the pole (I place the pole on a concrete block upright at the bottom of the hole before pouring concrete). Minimum length of the poles under the surface is 60cm or 2ft. Which turns out as a lucky advantage as at the start of the wall with the smallest height difference which I originally worked out at just 1 plank or 15cm high, it turns out that the wall needs to be a plank higher in this part as I removed all shrubs today. Then the wall will rise up to 120cm/4ft at its highest point at the other end, where it terminates to an adjacent building. I also found the remains of an old brick wall with its foundations today exactly where I planned the wall! But I use this to my advantage and move the new wall a bit further back, and the old foundation will be in front of the newly made foundations and help to keep the wall in place.

@@Tom-Lahaye I think your wall will stand for longer than you will!

@@madebyjnd I'm sure it will, btw I was wrong on the wood, it isn't bankirai but azobe, a very hard wood which can withstand being submerged in water.

I bet they were on flat ground and more than 650 mm from the side of a house.

The posts are leaning back about half a bubble on a spirit level or approximately 3 degrees.

The posts are hot dip galvanised I-beams with a 5-1/2 inch web. Very common in Australia as these retaining walls are everywhere. In the USA, probably only available by special order from a steel supply house. If you mean the concrete sleepers, you would probably need to cast them yourself. These were 4x8 inch x 6 feet long. They have three lengths of 5/8 inch steel rebar inside. Also very common in Australia, they come in 2, 3, 4 and 5 inch thicknesses, all sorts of lengths.

Do you know if the 5/8 steel is cross braced and what strength of concrete is used?

Hi Tim. The rebar is not cross braced, the three bars are merely parallel and spaced evenly. Concrete strength? No idea but I’d guess at least 3000lb

Jay russel if you mean drainage from atop the foot path, it has a slight 1:15 slope from the rear to the front of the house. if you mean from behind the wall, there is an ag drain along the entire length, again sloping from rear to front of the house. The ag drain is more or less redundant as the ground behind the wall slopes away from it. It doesn’t rain that much here and these two things have been more than adequate, never any puddling or standing water during even a cloudburst.

The ones I used were galvanised but standard uncoated beams should be available at any steel supplier. If galvanised beams aren’t available you should be able to find cans of cold galv paint and make your own. clean the mill scale off first before coating though.