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Retaining Wall ideas and drainage

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  1. #1
    Apprentice (new member)
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    Default Retaining Wall ideas and drainage

    Hi all,
    I've dug up my front garden area and want to put in 2 retaining walls in order to tier it (see pic 3).
    During our last big rain I noticed a lot of water coming from the central area of the retaining wall and bottom slab level (ie the carport) (see pic 1). Since I've dug up the bulk of this area it would make sense I try to rectify this problem also - Or find a work around to limit it.
    So I have 2 questions
    1) Is the likely cause of the leaking water due to a broken AG Line? Or would it be the fact that the AG Line isnt deep enough? Note that the AG Line does catch some water and drains it to the side of the house as planned. Its just the center area where it leaks.
    2) As I am tearing/stepping the dug up area would additional AG line at each flat section be beneficial? (see pic 3)
    3) I intend on using concrete sleepers (woodgrain) from retainease. given the fact i only intend on stepping down 3 sleepers per step (ie 600mm each step) would i need to set the base of the H Beams in concrete?
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  2. #2
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    Broken AG line...maybe or no AG line or blocked AG line and overflow is simply seeping through would be my best guess.

    Definitely an AG line behind each wall level with free draining rock such as scoria with geotextile over the top/sides to stop the soil over time seeping through the rock and blocking your drainage.
    I normally recommend plastic behind the wall if the wall has a path in front of it. In your case, its just garden (I assume) and therefor no need.

    If your using H beams with 600mm high wall, you will need to go down a min of 600mm deep x 350/450mm diameter....given your on a slope and depending on the soil, maybe more depth. They will need to be set in concrete. Just use a motar mix or concrete mix to set the level of the first row inside the H beams.
    If you plan to drain the AG lines out the ends, make sure you put a verman proof cap over the ends...obviously with drainage holes.
    Set the inside posts measurements to 15mm more than the concrete sleeper length, a piece of wood cut to length (sleeper length + 15mm) assist with this.

    Also check and confirm where your services run - Water, power, gas.

    Lastly just an observation: The sketch showing the levels.....just check the measurements as 3 levels with 2 walls of 600mm high falls short of 3000mm total height unless each level is battered back.
    This is potentially what it may look like....based on my interpretation of your sketch/photo's of the measurements and assumption of degree of slope - Green = original slope, Red = new back fill

    Attached Thumbnails Attached Thumbnails wall.jpg  
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  3. #3
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    Thanks Bart for the response. Much appreciated.
    I've had an idea over night.
    To save me from digging up behind the original timber post wall (ie digging up 10m X 1.1m high) in order to find the existing AG line that "could" be causing the issue would it be an option to simply lift a row of pavers along the base of the wall or next to the carport slab and install an AG line/drain there? and then proceed with the above retaining wall option as you've shown in your sketch but instead of installing each wall at 400mm high install at 800mm high (or 1000 high) to minimise the fall of each level?
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  4. #4
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    Ok....
    1) So ive dug it up a little and have come across the attached metal (copper) pipe that looks like it has been capped? It runs in the direction of where the is an electrical pit (approx 3m across and 3m up) so it isnt running directly to the pit but there is nothing else remotely in the direction this pipe is running? Any ideas?
    2) Also, the AG Line seems to be sitting directly on clay (or hard mud). Is that hiw it should be? Or should there be blue metal under also?
    Thanks
    Ed

  5. #5
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    Hey Ed, could it be water pipe from the meter position...or an older meter position. What size is the copper pipe - 12mm?

    Ag lines if done correctly behind retaining walls generally are laid on rock, with at least a 1/3 to 1/2 of the height of the retaining wall height such as yours filled with more rock and covered in geotextile to stop soil leaching into it and blocking it all over time.
    Plenty of info on the requirements.

    You may have your heart set on the duel retaining walls Have you considered just working with your current batter and landscaping it?
    Could use rocks that are forgiving on a bit of movement and plant up around them as a suggestion.
    Depending on what your after, could save you a s$%t load of effort


    ...some inspiration.
    https://www.pinterest.co.uk/pin/690387817848789936/
    Bl: Landscaping ideas hillside steps Guide
    https://homedesignlover.com/landscap...n-a-hill-tips/

  6. #6
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    Sorry,
    Pic attached.
    Attached Thumbnails Attached Thumbnails 20210601_170205_resized.jpg  

  7. #7
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    The more I look at it (and dig) I'm starting to think the most likely cause for the water running/leaking from the existing retaining wall in the specific area is probably due to blockage - as you initially said Bart
    The AG line isnt wrapped in a sock so maybe the soil has penetrated into it and caused the blockage and hence the leak in the middle (and not on either side).
    Another question, if we wanted to cut and replace a section of the AG Line is there a bracket or sock to join them?

  8. #8
    4K Club Member Marc's Avatar
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    Water behind a retaining wall will look for the shortest way out. Any number of slotted pipes will not stop water if there is a better, easier way. In other words, the drain behind a wall will channel the water providing the pipe is free of obstruction, has the proper fall, and there isn't another easier path for the water to breach the wall.
    The most common mistake when installing ag pipes is to chuck them in a trench behind the wall without regard to gradients as if it had some magical property to attract the water inside it.

    Another error is to believe that a permeable retaining wall, or one with a defective lining that allows water to escape will benefit from a drain. The water will chose the path of less resistance and that is invariably through a hole/ crack/ gap in the wall
    Whenever you find yourself on the side of the majority, it is time to pause and reflect
    Mark Twain

  9. #9
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    Quote Originally Posted by ed612313 View Post
    The more I look at it (and dig) I'm starting to think the most likely cause for the water running/leaking from the existing retaining wall in the specific area is probably due to blockage - as you initially said Bart
    The AG line isnt wrapped in a sock so maybe the soil has penetrated into it and caused the blockage and hence the leak in the middle (and not on either side).
    Another question, if we wanted to cut and replace a section of the AG Line is there a bracket or sock to join them?
    Assuming by "bracket" you mean joiner ?
    Depending on the type of pipe there are joiners
    https://www.bunnings.com.au/vinidex-...E&gclsrc=aw.ds
    And Sock by itself
    https://www.bunnings.com.au/reln-100...-pipe_p0210906

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