Installing a Ringwall on an Existing Tank

[AWDMIKE]

I've recently come across an existing tank where a ringwall was installed but had previously been supported at grade. The tank looked most unusual at first glance; the outer face of the shell was still mostly white with coating, however there were rust-colored lines in the longitudinal direction, as well as a few in the circumferential direction in a neat grid-like pattern. I was unable, at first, to determine why it looked like that (attached).

By chance, I saw a photo (attached) which was taken during the installation of a new ringwall on another tank, which had also been previously supported at grade. This photo shows a wide flange under a portion of the tank and the adjacent shell cut away. There is also a structural member of some kind welded longitudinally, obviously to assist in supporting the tank now that it was no longer supported by a circumference of shell.

My question is, with regard to the discoloration of the tank and installation of the ringwall. Is the grid-like pattern of rust-colored lines due to the fact that sructural steel was required to be welded to the tank to temporarily support it during the ringwall installation?

Additionally, and I understand there are likely several ways to perform this installation, but how is the tank jacked up and how it is supported while jacked up? Are there special hydraulic devices used at each location of a wide flange to jack and support the tank? Is the tank held in the jacked position while pouring most of the ringwall, backfilling the space within the new ringwall, and installing the new tank bottom? The new ringwall could not be completed before the tank was lowered back down, as the wide flanges would still be welded to the underside of the shell. I suppose most of the ringwall, backfill, and tank bottom could be installed while the tank was jacked up but excluding the areas where the wide flanges would need to recess to get the shell back to contact the new bottom. After the tank was lowered to allow the shell to approach the new tank bottom, the shell to bottom plate weld could be completed, the wide flanges removed, and the ringwall, backfill, and tank bottom be installed where the wide flanges were?

Any ideas are appreciated to help my understanding of this process.

 

[AWDMIKE]

I forgot to mention that in my post, above, that a lower portion of the bottom shell course was likely being removed, but thought someone would be able to confirm that from the picture. If the entire bottom shell course was being kept the same height, I would assume small openings in the bottom of the tank shell could be made to place the beams through. I say this because I've come across another photo which shows an existing tank on a new ringwall, previously supported at grade, with small 1 foot by 1 foot shell patches around the circumference of the bottom shell course at the base of the tank. This is presumably where the beams were placed to support the tank.

 

[IFRs]

I just designed jacks to pick up a 120' diameter tank while the existing foundation was demolished and a new one poured on the exposed piles. A new bottom annular ring was placed and the tank was lowered down. I have in the past participated in jacking to replace lower courses of steel or to add to the height of a tank. Where is your tank located (do you have an experienced contractor there?)

 

[AWDMIKE]

I have found these photos in our client's old inspection reports. The ringwalls were added some years ago, and beyond that I have no knowledge of who performed it or how it was performed. I was curiously asking to try to understand better what the process entailed and the order in which it was executed.