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How to build a fence over a concrete sleeper retaining wall?

How deep should I set my steel posts in the ground? and how do I slope/batter the steel posts backwards to provide additional strength? Is there an easy way to brace the steel posts in the ground ready for pouring? What is the best method to set the posts in the ground? I've heard just dropping the steel H/C posts into the concrete to height and letting it set is fine?

Advice would be appreciated!

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Comments

EricL

Hello @Naidoo021

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your installing a fence over your retaining wall.

I suggest having a quick look at this discussion - How to build a fence on a retaining wall by @mitchcasey. As a general rule, the hole depth should be at least one-third of the above-ground height of the post. For example, if your steel post will be 1.8 metres above ground, aim for a depth of around 600 millimetres. For taller structures or where wind loads are a concern, go deeper closer to half the post height if possible. The hole should also be wide enough to allow for sufficient concrete around the post, usually two to three times the post’s width.

However, the rules and regulations change when you are installing a fence over a retaining wall. The dynamics and interaction between the two structure changes and the installation becomes a bit more complex. Attaching a fence directly to a retaining wall, or placing it right behind the wall where it might affect stability, typically requires assessment by a qualified professional. This is because the combined structure can behave differently under load, especially in softer soil or if the wall is retaining a significant height.

I suggest engaging the services of a professional fencing installer or a structural engineer to ensure everything is done safely and within the right guidelines.

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you need further assistance, please let us know.

Eric

Dave-1

Good Evening @Naidoo021

Welcome to the Bunnings Community page, definently a good place to start with questions about retaining walls and fences 🙂

First up can you supply some pics? It would help us visulize what you want to do.

Now for your questions

Q1- How deep should I set my steel posts in the ground?

A1- I am also suggesting a 600mm deep hole as the starting point on a 1.8m high fence post. (that is level ground, no disturbed earth)

Q2- and how do I slope/batter the steel posts backwards to provide additional strength?

A2- I am a little confused on why you want to slope the posts like that, the 400mm retaining wall should be carrying the load, the fence posts you are planing on installing are part of the retaining wall?

Q3- Is there an easy way to brace the steel posts in the ground ready for pouring?

A4- The steel posts for the type of retaining wall you are building are purpose made and meant to be installed almost vertical I think. Having a slope involved will add a large complexity to it. (You can always make up an A frame with two pieces of timber and a cross piece that you wedge at the angled post for the angle you want)

Q4- What is the best method to set the posts in the ground?

A4- I would concrete the posts in the ground vertically. I would set the fence back from the retaining wall by 600mm.

Q4b- I've heard just dropping the steel H/C posts into the concrete to height and letting it set is fine?

A4b- Making sure that all the posts line up and are the same depth so no cutting the top would be what I would aim for. Having the posts vertical will lesson the chance of something being out. I always worry that the concrete sleepers wont fit between the post when I see someone installing them 🙂 Tho that may be me just over worrying.

I like using systems different ways then what they were meant to do :), with that comes a caution over pushing ideas too far. I think the diagonal posts are raising the stakes of issues that could arrise for you. 😕

Dave

Nailbag

Hi @Naidoo021

General rule of thumb is 1/3rd of post height goes in the ground.
Make the hole as small as possible. The bigger the hole the more concrete and the more $$$. Use pincers to make the hole. If it gets hard add some water to soften it and help it stick to the blades. Dont have to buy expensive pincers, just ones that don't smash your knuckles in use.
If the wall is going to actually hold serious weight I slant my posts slightly backward just a couple of deg.
I put some water in the hole then add the first bag of rapid set and stir it in before dropping the post in. Then add part water then part rapid set until the hole is filled. I have an old star-picket I use to stand and mix.
I'm constantly checking my levels as I go.

I usually rest a couple lengths on timber as once the posts are in for a little 3rd hand help. And I go light when adding the extra water and concrete. it's now a horse race. And make sure you're mixing the cement and water in well so there is no dry mix. This is why after the first bag I do it in gradients, especially with longer posts.

Hope that helps. Nailbag

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