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How to dig trench for ag pipe near retaining wall?

Hi All,

I've recently had the construction of my house completed and now got an empty backyard (full of weeds) which I would like to do its landscaping myself.

I've already killed all the plants/weeds using roundup and I'm planning to dig a trench all round my fence sides and back to place and ag pipe. Unfortunately, when retaining wall was done by a contractor, he advised that ag pipe is not needed but I don't feel that is the case, considering how heavily clay based the soil is.

Anyhow, the sleepers are affixed to wooden posts which are set into the ground using cement. I don't know how deep the go.

I would like to dig the trench but I don't know if removing soil from around these posts and retaining wall is a good idea. I'm concerned it might weaken the stability of the wall.

How close to the retaining wall should I dig?

Your help is much appreciated,

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Comments

MitchellMc

Hi @ArashM,

When it comes to digging the trench for the ag pipe, you'll want to be cautious around the retaining wall to avoid compromising its stability. Essentially, the trench should be dug just outside the concrete footers of the posts to ensure you aren’t disturbing the structural integrity of the retaining wall.

The goal is to allow proper drainage while keeping the posts and their cement foundations undisturbed. If you dig too close and expose the footings, you might risk weakening the posts and the overall structure of the wall, especially in clay soil, which can shift over time.

Also, since your soil is heavily clay-based, installing the ag pipe is a wise move to improve drainage and prevent water buildup, which can put pressure on the wall. Make sure to place the ag pipe at the right depth and grade to allow water to flow away from the wall effectively and towards your nearest stormwater pipe. You'll need a licensed drainage expert to make the connection to the stormwater.

If you’re unsure how deep the posts are or how wide the concrete footers extend, it might be worth digging a small test section to get a better idea of their placement before proceeding with the trenching.

Please let me know if you have any questions.

Mitchell

ArashM

https://www.workshop.bunnings.com.au/discussion/comment/43689#Comment_43689

Thanks Mitchell for your quick response.

If the neighbour is on higher ground, then me putting the ag pip next to my side of retaining wall would render it useless, correct?

I could ask the neighbour to put in ag pipe on their side but I don't reckon they'd go for it, considering cost of installation and dirt removal.

Also, forgot to mention, my soil is clay based but very rocky as well full of small and large chunks of rocks, not sure if that would make a difference. I've watered the ground few times and it seems to absorb quite quickly into the ground, I've only seen pooling so far where the retaining wall posts are because of concrete underneath

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/84112#Comment_84112

No, I wouldn't say it renders it useless @ArashM. To prevent water from passing through a retaining wall, it's best to put an agiline on the side where the water hits it, that being the neighbours. However, the next best option is to capture the water after it has passes through the wall, on your side.

Your agline will capture everything that passes through or under the retaining wall and prevent the area from becoming flooded.

Mitchell

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