Backyard Aquaponics
A place to discuss aquaponics

Yeah, I tend to think that round tanks could be slightly different..

When I was burying my IBC someone suggested that I would be in trouble if the tank was ever half empty and we had heavy rain, suggesting that the tank might float up when the ground was waterlogged..

This has never been a problem, and I doubt it would in Perth sandy soils.. Has anyone ever heard of this problem before?

Seen it happen around town a few years ago when they put the sewerage on... lot's of places had new septic tanks recently buried, then it rained heavily and they popped to the surface like corks......

Other than the smart ones that filled them

my sump floated once when it over flowed

EKB, I have no firm plans at the moment. Just doing my homework early regarding my next system....

Simon

Some of the differences in whether or not a plastic tank can take being buried underground is in its design. The smooth plastic tanks, whether rectangular or round, generally do not have the strength to take being buried underground unless it is filled with water before backfilling and then is kept full. Most plastic tanks intended for underground burial are ridged or corrugated. These add dimensional strength to the sidewalls, top and bottom, but might prove problemsome in getting adequate drainage and removal of fish poo and wasted food.

Around here all septic tank installers flood the tanks prior to backfill. It doesn't matter whether it is plastic, steel or concrete, they do it to prevent it from rising out of the ground if there is a heavy rain prior to the soil settling in around it.

Kevin

Buring plastic tanks is a tough thing to do with sucess. The best are a ball shape and will hold about 300-500 USG. They are designed to resist soil loading. Ever try to crush an egg bare handed? Okay, don't try that in the living room, just in case....
Attached is a drawing of a plastic tank we use for the Flout in a septic system. Works well, but without the ballist rocks or concrete pad, the water table may force an empty tank out of the ground, as others have stated.

Okay I've saved the file as a Word *.doc and a *.pdf file and cannot attach either to this message. Anyone wants a copy, send me a note and I will return the file by email.

your drawing should have ballast too coz it floated away

Off into Never Never Land....

Sparky... you need to "zip" the file... use either winzip or winrar

Then attach the zip file to the post.

AM and his AP students know all about this from practical experience

am sure if you shore it up it will be ok

Ah yup, they shore found that one out, didn' they!

Kevin

Sorely tested with that lot

I have a corrugated plastic 4500l tank buried for almost its entire height ( ie 1.35m tall buried about 1.2 m) and it seems fine. Logic suggests to me that unless you get hydraulic pressure from below the tank should be fine provided the soil is stable. I have heard of large concrete water tanks being pushed out of the ground after heavy rain but I expect they must have been close to empty at the time. When I decided to bury my tank I thought that I would fill the tank with water at the same time as I backfilled the soil but I didn't end up doing so. Backfilled then filled the tank with water- no problems. There is really no pressure on the walls of the tank from the surrounding soil, unless the soil is saturated with water, and so why would the tank collapse? And as long as the tank is full of water those pressures, if they occur, would be equalized.?
Needless to say we are not talking about tanks completely buried ie soil on the top as well- then feeding the fish would be somewhat awkward?

Jim, check AM's thread under Member's Systems, Lutheran Peace Students Get Going (click on the links above) and look at the first couple of pages. When he buried the tanks in the first system they collapsed on his students due to the soil being saturated with water. (Also soil type makes a big difference.)

Kevin