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Thread: water tank retainer wall

  1. #1
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    water tank retainer wall

    Need help. my 20,000L concrete tank is sitting near the edge of a bank which is slowly being eroded away. There is already gap between the tank and ground about 50-100mm deep and 1.5-2m under the tanks bottom edge. Its only a matter of time before the tank ends up down on the road and floods the neighbours property so I need something done to stop the erosion and support the tank like some sort of retainer wall? the tanks been sitting there for 20 years and I'd like it to stay there another 20 otherwise I'll have to invest in a new tank placed somewhere else and turn the concrete tank into a shed. So if there's someone who's got the expertise to give me advice and maybe a quote that would be great. Thanks.
    I'll post some photos tomorrow.

  2. #2
    Member 40mm's Avatar
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    If you have another source of water then drain it now, might buy you some time until the wall is built.
    Good luck.
    Use enough gun

  3. #3
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    buy new plastic temp tank to give time to drain and shift conc tank cheaper than wall with conc /pile costs etc 20000 lts = 20 tonne just the water so wall will cost mega$ .

  4. #4
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    Look forward to the photos.
    I am sure it can be done.
    Retaining walls can be built reasonably cheap and can carry a remarkable amount of weight.
    Just look at loading banks used for big equipment.
    Maca49, Moa Hunter and 40mm like this.

  5. #5
    John Galt Sr.
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    Yup. 20T static load is feck all.

    As said, draining would be best.

    If it can be lifted/ tipped out of the way to get a decent bed under also best. Unless it one dem corrugate/ ferrocement ones poured in place...

    Would need to see site. Could be cut in deeper, or a slope battered up to it instead of retaining.
    Mind you probably looking at less than half dozen posts so, not massive. Could maybe go gabbions, more labour (yours) less cost.
    Though maybe want to extend retaining for Mrs' raised garden or something at the same time...
    Maca49 and Marty Henry like this.
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  6. #6
    gun guy
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    Not my expertie but would a gabian basket work. Seen them used around here to stop banks eroding. No idea of the cost tho.

  7. #7
    Member 40mm's Avatar
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    As for back filling under the tank once the new wall is built.

    Build the wall 100mm higher than the base of the tank, box up around the tank.
    Fill as much of the void as you can with gap 65 or something you can compact (post rammer etc)
    Then pour a very, very runny concrete mix into what is left. Make sure to pour the concrete higher than the base of the tank and use a stick or hire a concrete vibrator to poke under the tank.
    Should make a solid bed for it.

    Before you invest any cash into this, drain it and throughly inspect the inside of the tank.
    Be a shame to spend all that on a stuffed tank.
    rugerman, timattalon and Borris like this.
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  8. #8
    Member rugerman's Avatar
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    Sounds a bit tricky, pics would definitely help. You say the bank is being eroded away, is this from the bottom of the bank or is water running along the top and then down the bank. A bit of drainage around the tank on the uphill side might reduce the erosion and buy you more time. Best to drain the tank before doing holes for posts around it etc... but if you may be able to drill some holes one at a time diagonally under the tank and fill with concrete to help stabilize the bank
    Moa Hunter and mimms2 like this.

  9. #9
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    I do have x2 fibreglass tanks, not sure if they're 2500L or 5000L, plus a 1000L I plan to set up this weekend to drain water from the concrete tank to ease pressure and reduce weight. There are cracks around the tank so it might be past its used by date?
    Here are some photos
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    rugerman likes this.

  10. #10
    Member rugerman's Avatar
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    Yeah it does look a bit precarious. I wonder if there is a crack in the feeding pipe causing water to leak near the base of the tank adding to the corner dropping a bit. If there are cracks in the tank, given it's position it might not be work mucking around with it. Depends how much a new plastic tank is I guess. I assume when the tank is full it overflows down the side of the tank right where the gap is under the tank ?

  11. #11
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    Quote Originally Posted by rugerman View Post
    Yeah it does look a bit precarious. I wonder if there is a crack in the feeding pipe causing water to leak near the base of the tank adding to the corner dropping a bit. If there are cracks in the tank, given it's position it might not be work mucking around with it. Depends how much a new plastic tank is I guess. I assume when the tank is full it overflows down the side of the tank right where the gap is under the tank ?
    @rugerman. Yes the tank is full and does over flow, the original installer should of put an overflow pipe running from the top of the tank down to the road. Don't know if the feeding pipe is leaking.

  12. #12
    Member rugerman's Avatar
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    Cracks in the tank not withstanding, It might not be as bad as it first looks. If the tank is overflowing and washing out the bottom corner, the rest of the ground under the tank may be sound. I assume the downpipe in the top is the feed from the house so if it's cracked in the ground it may be leaking when it's raining too. I would have a bit of a scratch around the base and maybe shine a torch in the low side and see how far back the slump goes.
    Moa Hunter and 40mm like this.

  13. #13
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    Hey, I'm too far away to even look at doing this, but there is a little more to it than what may appear. The bank below looks quite steep, static load is not huge, as long as the tank is level.

    2 options.

    1, retain the tank platform and ram gap20/pap7 under the tank. I would recommend posts 1200mm long 1000mm in ground (based on similar projects/loads). It seems overkill, but the slope is a killer.

    2, drain tank and move it. Probably not a super hard job, tank would weigh 4-6000kg?? Dig a pad behind it, flat as, and at the same level, get the local 4x4 club to get thier winches out.

    I have a soft spot for old concrete tanks, so try not to just break it up, though they make wicked smoke houses.

    If you do get someone to price doing it and you would like to make sure it's all above board flick me a message.

    Thanks Lars

  14. #14
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    Looks better than my concrete tank, still in use.

    Options for the crack side, once you have it stabilised are get a liner installed (cheap enough) or epoxy seal the cracks if they are bad enough internally.

    As far as the subsidence, that's actually not that bad an issue. Build a retaining wall out in front - a proper one anchored down quite deep with drainage across the front to prevent more slumping. Gravel etc in the hole stuffed in as far as, then pump grout in to finish the job. If that doesn't float your boat get the epoxy stabilisation injection outfit to quote.

  15. #15
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    Thanks for the input guys. Only reason I'm in a bit of a panick is because its gotten worse very quickly and the neighbour across the road is downhill from me and last thing I need is 20ton of water including concrete rushing into his backyard and flooding his house causing all sorts of carnage. My old man owns a digger so I might see if he can transport it to my place and push the tank back?

 

 

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