# Forum Home Renovation Retaining Walls  Hole size required for H channel retaining wall?

## gjws

Hi all,  I've done a lot of reading and have put together a 3D sketchup of the retaining wall I want to build. From my research I've found post depth should be half in half out as well and to use regular concrete not rapid set, but I haven't sound any recommendation on hole size and amount of concrete when using H channel. I'm planning on using a post hole digger for the H channel which will give me a hole diameter of around 200mm, will that be enough or should I aim for a greater diamater?  Also as far as concrete goes I planned on filling the holes to just below the top of the hole so I've got some room for backfilling with soil, does that sound right? Any suggestions would be very welcome!  Thanks.

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## cherub65

Really depends on soil type for hole size

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## gjws

> Really depends on soil type for hole size

  It's very sandy soil, I'm in the sand belt in SE Melbourne. When they dug the pool they had to support it with ply as it kept collapsing!

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## cherub65

what height are you planning to build? maybe there are better options

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## gjws

> what height are you planning to build? maybe there are better options

  Everything was delivered this afternoon so there is to be no mention of better options  :Smilie:  
It's only 600mm high, I've dug all the holes to 600mm and they are around 250mm in diameter. The C channel and H channel are all 1200mm so I'm 50% in and 50% out, I'll be mixing up the concrete and installing the channel tomorrow, then installing the sleepers on Tuesday. At this stage I can easily make the holes larger, once the H channel is in there I must admit it looks quite full. I don't want to go overboard however, it's not really very high. 
Thanks for you help.

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## cherub65

Would do min. 400 x 400 x 600mm, set posts with slight incline back

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## stevoh741

Your hole size and depth is fine. At 600 high it's barely more than a raised garden bed. Make sure drainage is correct behind the wall and you will never have a problem.

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## gjws

Thanks for you feedback guys, much appreciated.

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## carshi

600mm is not so high, your hole size should be fine.  I would have gone 700 to allow for 100m of scoria at the base to allow for drainage so water can drain.  Wont really matter if you havent done it, the depth will be good enough.  Make sure you dont make the concrete level the hole as it is a pain when trying to get them to sit right.

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## XESP351

I have undergone this exact same project about a year ago....600 mm high wall out of 75mm thick redgum sleepers...because the wall is only 600mm high and isnt really retaining much, it's against a fence, I used 1 m beams and had 400mm in the ground, concrete about 300 mm high, holes varied in size depending on how tired i was on the day (clay and rock soil). The wall is still solid as a rock and looks sensational after sanding and staining.

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## barossa

I've followed loads of threads on this issue and have a simple question. 
I'm building a 10m long x 1m high retaining wall - retaining makes it sound more structural than it really is as its probably more cosmetic as the banking is structurally fine without a wall but ugly. 1m up = 1m holes with 200mm x 75mm sleepers. Posts wil be at 1500mm spacing. So heres the question - will wooden sleepers warp? The guy that put my road in and another than built the shed said Ishould use concrete sleepers as they last longer and don't warp. Concrete sleepers seem way too much like overkill, are expensive, and heavy for a 1 man job. Any advice? Thanks
Forgot this bit - hole diametre. Soil = quite heavy clay. 300mm holes or 450mm?

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## Joshwaaaa



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