Below grade concrete engineering help


Hi everyone. I am trying to work through plans of a 12x16 ft greenhouse. It will have a concrete foundation pored, but here is the tricky bit. I need a 10x4x3 sump chamber below the foundation. I live near houston and we have a very high water table. The concrete sump must be water tight (will contain fish). The foundation will be poored 1 foot below grade. That puts the bottom of the sump 4 feet below grade. Don't ask why or suggest alternatives, I really just need help making this design work.
My thoughts are to dig the sump, poor the 10x4 foundation. Build forms for the sump walls and pore them all in one go.
When pooring the actual greenhouse floo,r poor on top of the sump such that there will be a 10x4 hole in the floor looking down into a 3 foot concrete hole
Block walls will be built up from there and water proofed. When done, it should resumble a pond in a greenhouse.
The floor when complete will contain (if I did my math right) up to 13 tons of gravel and water.
My concerns are the stress between sump and floor and potention for cracking.
Questions: How thick do I need to make my lower and upper foundations. How thick do I need to make the walls of the sump.
My gueses are with enough rebar 8 inch foundations and 6 inch walls. I just really do not want the sump to "break off".
I also assume if I do this myself it will take quite a bit of time and I'll have to be concerned about it floating up out of the gound like an empty pool. The only thing I can think of is to leave an open drain and let it flood if needed. Once the sump is rendered and water proof, it can be permantly flooded.
Thanks for any help! Mark
PS And for those that cannot help but ask, this is part of a larger aquaponics system.
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Without asking why _and_ suggesting alternatives, people won't be able to help you and your design won't work. It's clear from what you've written that you don't know enough about concrete construction to tell a good answer from a bad answer, and you're asking a bunch of random people on Usenet for help. This is not a good way to proceed.
R
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Concrete does not lend itself to a monolithic pour like you describe. The right angle intersections at the bottom and top of the pond walls are very subject to cracking. These conditions are usually better dealt with by deliberate sealable joints or various waterproof seals a bit like these: http://www.greenstreak.com/div3/Waterstops/pvc.asp
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I wont ask why, but you dont need a sump or a tank or fish, its a greenhouse for plants with a floor made to drain water , its not carpeted. I have one also, it leaks from above and I dont care at all.
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Separate the pours. I believe that is what you have planned..... Expect some expansion and contraction between floor and sump. This would be better than having a crack form @ sump and floor. Sump would be height of floor....curb of sump. Also a pond membrane could be used in the sump. My question is: If it is a sump watertight as origninally planned where would water come from. (watering greenhouse?) Anyway, I have poured "hot tubs" and the use of steel would be important in the pour. A vibrator also to make sure voids are handled properly. I imagine you are planning drains and filtering piping in the sump. Sounds interesting.... I have a large concrete foundation greenhouse although no sump. Walls are 10" and about 6' tall on 3 sides to contain heat........heat sink. no pond though. jloomis

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*I'm not an expert on this, but a thought did occur to me. Why not have the sump prefabricated by a concrete casting company? Then you can seal it on the outside and just drop it in the hole and pour concrete around it.
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If you are a bit flexible in the shape/size, make some phone calls and you'll probably find a concrete place that has pre-cast box cheaper than contracting a custom one - i.e. burial vault, drainage box, septic boxes, etc., etc.
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I had the same thought, been looking around for place that sells precast concrete boxes. Have not had a lot of luck so far. I would go with a fibroglass or plastic sump, but tree roots are a big concern. Concrete bocks would be my prefered method of construction. I'm leaning tward that now, with a couple inches of fibromix to seal it up. There are so many methods of pond construction out there, it is hard to determine what is best for me.
Thanks Mark
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On Sat, 12 Dec 2009 06:34:04 -0800 (PST), DejaVoodoo

One would think in Texas there have to be many! Around here (New England) most larger towns have at least one place.

Why? Roots are not likely to penetrate plastic unless they 'know' there is water there.

Ug... I personaly would not do that.

Talk to some place that makes swimming pools and ponds.

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I found 35 precasters in the Houston area, follow this link to The Blue Book. http://www.thebluebook.com/ Select your area, then under Keywords ,type concrete, then follow down the list until you find conctete- precast.
Tom
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I thought of that but was having trouble finding anyone who does it.
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"> > Hi everyone. I am trying to work through plans of a 12x16 ft

I thought of that but was having trouble finding anyone who does it.
* http://www.precast.org
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