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Ridgi Retaining Wall

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  1. #1
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    Default Ridgi Retaining Wall

    Hi everyone,

    Advance happy holidays and with that, what a good way for some of us to work on stuff during the long holidays with no to less interruptions (e.g. work).

    Anyway, I am planning to put up a 30 centimeter retaining wall in our 4 meters x 7 meters front yard. I'm looking at stacking two Ridgi sleepers as shown below:



    A few questions:

    1) With that height, would I still need to put drainage behind the wall? I've seen raised garden beds higher than that and had no issues. The front yard has clay soil and currently sloped a bit (~ 7 degrees). I'm planning to fill it with garden soil after for planting.

    2) The installation guide suggests a generic hole diameter of 30 cm for all wall heights. So in my case, that would translate dig a hole 30 cm (diameter) x 40 cm (depth) for a post. Will that be an overkill if the post will just be sticking 30 cm high? Would a 15 cm - 20 cm diameter hole suffice so the the post won't have too much setback from the foot path and so as not to waste too much concrete?


    Cheerio!
    Attached Thumbnails Attached Thumbnails retaining-wall-02.png   retaining-wall-01.jpg   retaining-wall-03.png  

  2. #2
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    There are 2 ways to do what you propose.
    The right way and the right way.

    Of course you can dig the hole 150-200 and watch over time as the wall falls over, or you can do it the right way.

    And yes, you still need drainage.

  3. #3
    1K Club Member havabeer's Avatar
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    Dont skimp out on like $50 worth of concrete and have the wall tip over because you decided to not dig the holes deep enough. I'd go 30 - 40cm depths at a minimum
    Remember if you don't sin, then Jesus died for nothing

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    Quote Originally Posted by cyclic View Post
    Of course you can dig the hole 150-200 and watch over time as the wall falls over, or you can do it the right way.
    I see, I was just wondering if there's a sweet spot for the diameter hole. I mean, I can even go bigger but hoping I can have a sense of why does it have to be 300 mm. I believe the general rule of 3x the post size is applied here but since it is a PFC/UC beam, I'm thinking if it's an exception and if it can go slimmer as there is concrete within the post due to it's just beam design.


    Quote Originally Posted by cyclic View Post
    And yes, you still need drainage.
    I'm thinking of putting an agi pipe with sock along the lower sleeper behind the front wall. How do you guys execute the disposal of collected water? Do I just make a hole on one of the sides of the lower sleeper on one side for the water to exit? Sorry for the question as I haven't seen much videos showing how that part it's done.


    Quote Originally Posted by havabeer View Post
    Dont skimp out on like $50 worth of concrete and have the wall tip over because you decided to not dig the holes deep enough. I'd go 30 - 40cm depths at a minimum
    Yup, I would still go with the required depth and I'm just thinking of the diameter. If I try to consider the cross section of post-hole ration on the following:
    #1 100 mm post on a 300 mm hole - area ratio of post to concrete is .01 m2 (post) : .06 m2 (concrete) or 1:6
    #2 100 x 50 mm I-beam (3mm thick) on a 300 mm hole - area ratio of beam to concrete is .001 cm2 (I-beam) : 0.07 m2 (concrete) or 1:70
    #3 100 x 50 mm I-beam (3mm thick) on a 150 mm hole - area ratio of beam to concrete is .001 cm2 (I-beam) : 0.017 m2 (concrete) or 1:17

    On #3 with the 150 mm hole, it still has a better ratio than the 100 mm solid post to a 300 mm hole OR I might be just thinking too much

  5. #5
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    Quote Originally Posted by jarod View Post
    I see, I was just wondering if there's a sweet spot for the diameter hole. I mean, I can even go bigger but hoping I can have a sense of why does it have to be 300 mm. I believe the general rule of 3x the post size is applied here but since it is a PFC/UC beam, I'm thinking if it's an exception and if it can go slimmer as there is concrete within the post due to it's just beam design.



    I'm thinking of putting an agi pipe with sock along the lower sleeper behind the front wall. How do you guys execute the disposal of collected water? Do I just make a hole on one of the sides of the lower sleeper on one side for the water to exit? Sorry for the question as I haven't seen much videos showing how that part it's done.



    Yup, I would still go with the required depth and I'm just thinking of the diameter. If I try to consider the cross section of post-hole ration on the following:
    #1 100 mm post on a 300 mm hole - area ratio of post to concrete is .01 m2 (post) : .06 m2 (concrete) or 1:6
    #2 100 x 50 mm I-beam (3mm thick) on a 300 mm hole - area ratio of beam to concrete is .001 cm2 (I-beam) : 0.07 m2 (concrete) or 1:70
    #3 100 x 50 mm I-beam (3mm thick) on a 150 mm hole - area ratio of beam to concrete is .001 cm2 (I-beam) : 0.017 m2 (concrete) or 1:17

    On #3 with the 150 mm hole, it still has a better ratio than the 100 mm solid post to a 300 mm hole OR I might be just thinking too much
    300, I assume, is the engineered size, so go with it.

    50 ag without sock will do the job for such a small wall.
    If possible, simply let the ag run out under the lower sleeper.

    I will let havabeer use the calculator for the holes.

  6. #6
    1K Club Member havabeer's Avatar
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    I think it's probably because ease of toolage.

    Nice standard 300mm auger. Rather then 275 or 330
    Remember if you don't sin, then Jesus died for nothing

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    4K Club Member Marc's Avatar
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    I see, I was just wondering if there's a sweet spot for the diameter hole. I mean, I can even go bigger but hoping I can have a sense of why does it have to be 300 mm. I believe the general rule of 3x the post size is applied here but since it is a PFC/UC beam, I'm thinking if it's an exception and if it can go slimmer as there is concrete within the post due to it's just beam design.
    The diameter of a post footing is related to the load. In your case the vertical load is negligible and all it matters is the lateral load. A round hole makes sense if you are going to use a motorised auger. If you are going to dig by hand, make the hole square with a flat side facing outwards. That is the one that will keep your post vertical. 300 seems a good size and I would go 400 deep.

    As for drain, 50 mm agi pipe is rather pitiful, you have a substantial area on impermeable clay so your garden water will go through the garden soil quick and hit the clay and look for an exit. Use a large pipe, and cover with blue metal or recycled concrete < 10mm. I agree not to use a sock over the pipe, they clog too easy. Nice project, but ... any reason to use that system over garden blocks? With them you need no footing and no drain, just plonk them on a bit of road base ... well may be a bit of aggregate behind them if you must.
    And if they move, just kick them back in line
    Enjoy present pleasures in such a way as not to injure future ones.
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    Quote Originally Posted by cyclic View Post
    If possible, simply let the ag run out under the lower sleeper.
    I've seen this suggestion before but I'm finding a hard time to visualise this. If it's under the lower sleeper then how would that end up on clay soil? Or would it go under the sleeper and up again then connected to a pop-up valve on ground level?

    Quote Originally Posted by havabeer View Post
    I think it's probably because ease of toolage.
    That's what I'm thinking as well. Since I'm flexible as I'm digging my hand, I can do whatever is the recommended minimum and practical size.

    Quote Originally Posted by Marc View Post
    If you are going to dig by hand, make the hole square with a flat side facing outwards..
    If I'm doing it square, would it require a smaller hope than 300 mm then?

    Quote Originally Posted by Marc View Post
    any reason to use that system over garden blocks? With them you need no footing and no drain, just plonk them on a bit of road base
    That is actually my first option. I was looking at the Adbri Versalock before. I researched about them and found that it would still require me to dig a trench for road base then concrete on top before I can lay down the blocks. Otherwise, they said that it might move with the soil and crack - please correct me if I'm wrong.

    Also, what's the reason behind them not requiring drainage? It's it because they're permeable or because water can just go their the joints on the lowest blocks?

  9. #9
    4K Club Member Marc's Avatar
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    I was thinking in a block like the Keystone from Boral or similar. It's a big solid block that interlocks with a pin to the row below and works because of large mass. For a low wall like yours, a shallow trench with some road base in it would be enough and clearly no drain required do to the joints being open. The wall uses no mortar and no concrete footings. i fill the voids between the bricks with aggregate to give it some additional drainage. The blocks are on the heavy side at 30+ kilos from memory but they make for a fantastic retaining wall.
    https://www.boral.com.au/products/pa...walls/keystone
    Enjoy present pleasures in such a way as not to injure future ones.
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  10. #10
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    Quote Originally Posted by Marc View Post
    I was thinking in a block like the Keystone from Boral or similar. It's a big solid block that interlocks with a pin to the row below and works because of large mass. For a low wall like yours, a shallow trench with some road base in it would be enough and clearly no drain required do to the joints being open. The wall uses no mortar and no concrete footings. i fill the voids between the bricks with aggregate to give it some additional drainage. The blocks are on the heavy side at 30+ kilos from memory but they make for a fantastic retaining wall.
    https://www.boral.com.au/products/pa...walls/keystone
    Our 10 foot retaining wall collapsed 4 months after purchasing our new family home during a flood, it was a nightmare. Fiscally we couldn't afford the 190k (best case scenario without any further damage during reconstruction) quotes and our insurance wouldn't cover it. We learn't a few lessons:


    1. Drainage is king - invest as much in making your wall drain well as you do making it look pretty or you'll face the same issue in a few years time.
    2. Hire an excavator <-- and time your heavy lifting to be done in blocks of 1 day sprints. Will save your back and your sanity. I'm in Australia, the guys linked were a great source of local owner/operators wet/dry hire. We set aside every Thursday to have someone onsite for 5 hours to do 90% of the legwork for us and it wasn't prohibitively expensive in the grand scale of things.
    3. Doubling up on #1 - Behind your aggregate put a drainage mat - it will stop sediment from filling the gaps in your aggregate and eventually spilling out over your wall or even clogging the drainage holes you've left - this step will add 5-10 years to the lifespan of your retaining wall.
    4. Did I mention drainage? I feel I should mention drainage.

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