How do I replace rotting retaining wall posts?

[TandT]

Hi

hoping for some advice.

I need to replace a rotting timber sleeper retaining wall and the new wall needs to follow the same line as the existing wall. Therefore my new posts will have to go in the same places as the old ones.

My concern is that the old posts are large (they are pieces of sleeper) and are set into a  LOT of concrete, so digging them out will leave much bigger holes than the new galvanised posts will require.

What is the best approach to ensure the new posts are strong enough to support the new retaining wall? Do I just use heaps of concrete to fill the holes, or can I fill the old holes with soil, compact it as best as possible then re-dig more appropriate sized smaller holes to cement the new post into? Will the second option risk being too unstable due to being in disturbed earth?

Thanks for any advice about this!

The retaining wall is only 400mm high, and the earth behind it is very stable and not active in any way (it doesn’t get walked on of driven on).

[MitchellMc]

Welcome to the Bunnings Workshop community @TandT. It's brilliant to have you join us, and many thanks for your question about installing retaining wall posts.

Would it be possible to offset the sleepers so the post hole location is in between the current posts? If you plan to use these H joiners for your posts, you must cut the sleeper in half for the mid-join. You'll need to start with a first length shorter than the others to offset the posts, but the installation should be straightforward.

You could dig out the current posts and concrete, backfill with soil and then compact it. You'd then be right to dig new holes suitable for your new smaller posts. That sounds like a heap of work, and I'd be trying to come up with any other solution than digging out the current posts.

Mitchell

 

[Noyade]

My two glasses of wine thought is to weld up brackets from steel plate and gal posts with a mounting plate that straddles the rotted hole left by the vertical sleepers. The new horizontal sleepers would be bolted forward of the drilled steel plates. Possibly it might look quite nice? Illustration wise I cannot compete with my good friend Mitchell.

*hic*

Never drink and Doodle

[TandT]

Thanks for this info Mitchell, 

The offset idea could work for the intermediate posts. It'll still leave me with the corner posts (the wall has 2 corners) and 1 of the end posts that will absolutely have to go into existing holes. SO thank you also for the confirmation that it is okay to fill and compact the holes then re-dig smaller holes to cement the new posts. It's still a bit of work, but not as much as I was going to have to do! 

My next question will be whether or not I can cut the composite sleepers I'm hoping to use. They're a Bunnings stock item (Fitta Composite Sleepers) They look to me as if they should be able to be cut with a metal cutting disc. Do you know if they can Mitchell? No worries if you don't because the Fitta Rep is apparently going to be at my local Bunnings this Friday so I can ask him or her then.

Thanks again

Tim 

[TandT]

So wine is your creative thinking drink hey?

Works for me too, though scotch or beer are my more frequent choices. 

Thanks for the creative idea....unfortunately I can't weld. Maybe when I dig down to the cement and find our exactly how big the mass is I'll decide it's time to learn and give your method a crack! 

Thanks again

Tim

[MitchellMc]

Hi @TandT,

My only concern with cutting the sleepers down would be that they have a plastic component. I'd imagine a metal cutting disc would go through them fine, but it could get a bit clogged. Did you have a link to the product you'd seen in stock? I can't find any currently on our website.

Mitchell

[TandT]

Hi again @MitchellMc 

I don’t have a code, but there is a photo of the brochures of the 2 different products I’m considering.

The Fitta product on the left is my preference because it’s lighter so easier for me to work with as a DIY job, and I figure if I can cut it I’ll be able to cold galvanise the metal in it and re-seal the cut end of the sleeper to minimise rust issues in future.

the Ridgi product is concrete, so heavy and would be a nightmare to cut (plus I’m thinking cutting could compromise the reo bars I assume are in them and so would lead to cement cancer, ie rust and weakness over the decades that I want this wall to last).

very happy to hear your thoughts on any of this and REALLY appreciate your replies to date.

Thanks 

Tim

[Noyade]

Afternoon @TandT 

"Maybe when I dig down to the cement and find our exactly how big the mass is I'll decide it's time to learn and give your method a crack"

Yes, that's what I was thinking - trying to make use of your existing concrete. I made brackets outta scrap pipe and plate years ago that were bolted to an existing concrete edge surrounding a front garden. With concrete bolts there is immense holding power. Even some of the existing brackets at Bunnings may suffice - if there is enough concrete under the pebbles, seen above? But probably not if you're not going with treated sleepers again. I do think if you have crack at welding, you'll never look back as it opens up so many possibilities. Good luck with your project! 👍

Bolted to existing concrete edging.

[MitchellMc]

I believe they could be both special order products @TandT. I'd be happy to contact Fitta after the weekend to find out if you can cut their product.

Mitchell

[TandT]

Thanks @MitchellMc 

that’d be great if you were able to find out for me.

Thanks for the offer.

Cheers

Tim