Tank Foundation Cold Weather Impacts

[mark4lte]

Hello everyone,

I have been asked for advice on one of our "water" tanks on our plant site. We are located in North Dakota and it is the middle of winter (low 30's this week so not very cold for us). This is a 142' diameter x 40' high tank set on a ring wall foundation and was built back in the early 1980's.

The tank has been empty since last summer and now one of the process engineers have informed me that they will be filling it shortly with warm water (80 degree Fahrenheit). I was asked if filling the cold tank with the warm water would have any negative impact on the tanks foundation. My thought is "absolutely not; why would it?" I think the correct question to ask would be "would this have any negative impact on the tank shell" (which would be a question for one of our mechanical engineers).

Does anyone see something that I don't?

Thank you!

 

[jayrod12]

What is the ring wall supported on? piles or shallow footings?

If the latter, then there could in theory be an issue if the ground below the footing has frozen. If the former, then likely no issues.

 

[mark4lte]

It is indeed supported on a shallow footing 4' below grade. However, the drawings indicate that there is crushed stone extending from the base of the tank to 8' below grade (which is our frost line depth on site). The stone also extends out 9' from the tank perimeter. We didn't have a wet fall so there shouldn't have been any significant moisture within that stone layer before winter hit.

 

[racookpe1978]

Tank would have to be supported properly through several winters - not all of which will be as warm as this has been so far. 142 dia by 40 high will take a while to cool, but it is only 80 deg F starting. The ring wall will (try to) expand radially, so the expansion forces will try to twist the top of the support (heating from near 0 or less air temperature) up to 80 degrees quickly. Then, as it sloooooooowy cools, the ring wall foundation will slowly pull back to vertical. You'll see the gap this creates between the ring wall and dirt on the outside - that could plug up or leave an opening or snow or ice to fill, melt, and refill. Long term effect? Not sure. Best if you can keep it covered to prevent water or rain fro gettig into that space. The loose rock said to be there may help this movement from being a problem.

What happens when the water freezes as it is left in place for several days?

 

[mark4lte]

Thanks for the quick replies.

racookpe1978, when you refer to the cooling of the tank are you assuming that after the warm liquid enters the tank it will remain stagnant? The tank contains stripped gas liquor which is used throughout our cooling water system as well as other places (I don't have much more detail than that) so this tank level is constantly rising or falling. So, if the tank is being mixed after it's put back in service do you think the wall would contract back significantly? If a "large" gap is noticed we can certainly provide cover to prevent water or anything else from entering the void. The stress from the concrete's tendency to expand is really what worries me. I guess my question is should I have operations wait until spring to fill this tank? I know that maintenance & operations need to drain and clean the adjacent tank and waiting would set them back.

 

[bimr]

Removal of wet and weak material underneath the tank and foundation and replacement with a clean and draining aggregate would transform the ground into non-frost-susceptible ground and minimize the frost heave. Probably what the tank foundation designer would have intended on the project. See the attachment.