Hi everyone, I am looking for advice and experiences from anyone who replaced a single rotted sleeper & vertical post on a timber retaining wall. As you can see from the attached photos, the rest of the wall seems okay. The very bottom sleeper decayed & white fungi is building on where it meets the concrete path. When it rains, we get a messy runoff of black water onto the path. I thought I can do this over a couple of a dry weekends and replace only the bottom sleeper one section at a time. The steps I found online so far are: * Dig a narrow trench directly behind the bottom sleeper * Remove the rotted piece * Install a new H4 treated pine sleeper * Line the back with a geotextile drain fabric and backfill with 10-20mm drainage gravel to trap the mud and let water escape Before I head to Bunnings to grab the materials, I’d love to know: * Has anyone done a similar job, and do you have any tips? * For those who have dealt with mud bleeding out like this, did the geotextile fabric and gravel completely solve the issue for you long-term Appreciate any tips, lessons learned, or advice you can share Thanks in advance.

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How to replace a decaying base sleeper on a timber retaining wall?

Maya_m

Hi everyone,

I am looking for advice and experiences from anyone who replaced a single rotted sleeper & vertical post on a timber retaining wall.

As you can see from the attached photos, the rest of the wall seems okay. The very bottom sleeper decayed & white fungi is building on where it meets the concrete path. When it rains, we get a messy runoff of black water onto the path.

I thought I can do this over a couple of a dry weekends and replace only the bottom sleeper one section at a time. The steps I found online so far are:

Dig a narrow trench directly behind the bottom sleeper
Remove the rotted piece
Install a new H4 treated pine sleeper
Line the back with a geotextile drain fabric and backfill with 10-20mm drainage gravel to trap the mud and let water escape

Before I head to Bunnings to grab the materials, I’d love to know:

Has anyone done a similar job, and do you have any tips?
For those who have dealt with mud bleeding out like this, did the geotextile fabric and gravel completely solve the issue for you long-term

Appreciate any tips, lessons learned, or advice you can share

Thanks in advance.

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JacobZ

Hi @Maya_m,

Welcome to the Bunnings Workshop community, it is wonderful to have you with us.

The process you've described is spot on, but there is one key detail I would change, and it may just be down to how you've worded it, but I would not be digging a narrow trench, I would be digging a relatively wide trench. The reason for this is that the soil would be unsupported and if you are working in that trench, there is real potential for the soil to collapse, which could cause injury.

At that soil height, I would be digging back at least 600-800mm and installing temporary shoring to help retain the soil while working in the trench. A sheet of formply with some star pickets to anchor it in place is a common method for temporary shoring.

After digging back and installing shoring, your process is more or less what I'd recommend. Replace the sleeper with one of the same size and thickness, drape geotextile membrane over the trench and up the back of the wall, then fill with drainage gravel. It would also be best to include some agi pipe inside the gravel and run it to a drainage point, preferably a stormwater pipe, noting that connections to storm water pipes must be done by a licenced plumber.

This is the accepted standard for all simple retaining walls and will do a good job protecting the sleepers from decay and erosion through the wall.

Allow me to tag some members to see if they have any thoughts or similar experiences they can share- @Dave-1, @TedBear, @DIY4Knuckleheds, @diy_hausdesigns.

Jacob

Dave-1

Good afternoon @Maya_m

I agree with your suggested steps and definitely factor in a wider trench behind the wall. I am not sure where you will store the soil that you dig out but to stop double handling it I wouldnt just dig and throw it over the back of the area :) I have done that when i was installing a new retaining wall and ended up having to shift the soil 3 times all up lol

I would check the rear of the existing beams as you dig down and asses if they also need replacing. Even if another few years of use its a pain to dig the ground out again. Drainage is something I would install for sure. The brown water seeping out I think will still happen, less so with the ag pipe in place but still its fines in the water.

Dave

DIY4Knuckleheds

Hi Maya_m, The advice given by JacobZ is spot on. Go with that and you cant go wrong 👍

Maya_m

thanks @DIY4Knuckleheds @Dave-1 @JacobZ for the advice, can you recommend an agi pipe for drainage? Do you have any pictures on how these pipes are installed?

Maya_m

I found this photo online,is this how an agi pipe goes and do I need the black box at the left?

MitchellMc

Hi @Maya_m ,

The photo you found is a good example of the general idea. The agi pipe is typically installed along the bottom of the trench, directly behind the retaining wall, and then surrounded with drainage gravel. The geotextile fabric is wrapped around or laid over the gravel to stop soil washing into the drainage layer while still allowing water to pass through.

You don't necessarily need the drainage pit (the black box on the left of the photo). It's only required if you're collecting water at a specific point or connecting multiple drainage lines together. For a simple retaining wall installation, the agi pipe can simply be laid with a slight fall so it drains to a suitable discharge point.

If you intend to connect the agi pipe into your property's stormwater system, it's worth noting that this is regulated plumbing work and will need to be carried out by a licensed plumber.

For a straightforward drainage setup, this guide on How to install garden drainage shows the basic principles and may help visualise how everything fits together:

Please let us know if you have any other questions.

Mitchell

Dave-1

Good morning @Maya_m

This is the type of ag pipe I used under my pavers, it is slotted and socked to stop fines from entering the pipe as easily.

Ag Pipe

Here is the project where I used the slotted ag pipe to take water away. The slotted ag pipe section is at the end of the project :)
Fixing water ingress issues into the garage

Dave