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Hi,
I am planning to re-build a retaining wall that is going to be 700mm high. Replacing two steps of rotting retaining wall with one (See attached picture). I am planning to use 75MM X 200MM treated pine sleepers. I have couple of questions.
1. What combination of treated pine sleepers can be used to achieve 700mm height. There are only 200MM sleepers available in 2.4M length. What are my options to get that additional 100MM over 3 sleepers.
2. This new retaining wall is going to sit 600MM behind an existing retaining wall (newly built by previous owner). This existing retaining wall is 400MM high. Is this ok to build this way?
3. How deep should I dig for the new retaining wall given 400MM under it is already being hold by existing retaining wall.
Hello @jacksumit
Welcome to the Bunnings Workshop community. It's a pleasure to have you join us, and thank you for sharing your question about your retaining wall.
The traditional rule of thumb for the posts is half in half out plus 100mm, depending on the height of your retaining wall. So if the height of the wall is 700mm you will need a post that is 1.4meters long and a post hole that is 800mm deep. That extra 100mm is for gravel. This serves as water draining material for the bottom of the post. I recommend a width of 300mm diameter for the size of the post hole.
You could dig a channel that is 100mm deep so that half of the sleeper will be in the ground. This will give you your extra 100mm rather than rip cutting a 200mm sleeper which you'll then have to seal. So the set-up will be four 200 x 75 sleepers which gives you 800mm, but one of them will be half-buried in the ground to achieve the 700mm height you're after. Please note that it is always good practice to check the rules and regulations of your local council concerning the height of your retaining wall.
If the bottom of the new retaining wall will be starting from the level of the old retaining wall, the rule of half and half still applies.
If you have any other questions we can help out with, please don't hesitate to post them.
Let me tag some of our experienced members @ProjectPete, @tom_builds, @JoeAzza and @TedBear for their recommendations.
If you need further assistance, please let us know.
Eric
