How deep do steel posts for retaining wall need to be?

[Yeshe]

HI ,

I will be building a sleeper retaining wall 600 high. Using concrete sleepers and steel posts. How deep do I need to concrete them in? I'm thinking 600. If I add fence brackets and add a fence 1.4 high , how deep do I need to dig in then?

Thanks Y

[EricL]

Hello @Yeshe

Welcome to the Bunnings Workshop community. It's fantastic to have you join us, and thank you for sharing your question about your retaining wall.

The rule for retaining posts is generally half and half. If your retaining wall is 600mm you must dig a post hole of the same depth. However, the rule for fencing is 1/3 the height of the fence post. Therefore if the fence post height is 1400mm, the fence post hole must be at least 467mm.

I suggest speaking to a registered builder to double-check your figures, especially when attaching a fence above the retaining wall. The diameter of the hole you'll be digging will also need to be taken into account because of the fence you are attaching to the retaining wall.

Let me call on our experienced members @Adam_W and @ProjectPete  for their recommendations.

Please keep us updated with your progress, we look forward to seeing the start of your retaining wall.

Eric

[TheHandySqirrel]

Hi @Yeshe,

@EricL is on the money. The general rule is "what is above ground goes into the ground" when it comes to digging holes for posts. It's not a hard-and-fast rule though. For example, I have compromised for the posts of my retaining wall in clay and allowed for 3/4 depth as we have very hard clay. With concrete sleepers (I'm using wood) you should consider carefully any compromises though as you'll have much more weight.

Do consider drainage as well, wet retained soil causes a lot of walls to fail if they don't drain it away.