Tank settlement -Reworking Foundation apron

[DBreyer]

Hello all,

we have an atmospheric storage tank (fixed roof, gasoline) that has somwhat settled over the years. Now the chime area has a lower elevation than the apron of the foundation (compacted gravel foundation with bitumen/sand cover; apron covered with asphalt).
This prevents free draining of rainwater away from the tank. It accumulates atop the chime and could (if the seal between chime and apron (bitumen) has failed) flow underneath the tank bottom.

One option we are lookig at is reworking the apron (remove asphalt and top layer of gravel, put new asphalt on, seal chime to apron) to allow free drainage again.
What is your experience doing that?
We would like to do this with the tank in service. Do you see a risk for a foundation failure and subsequent risk for the tank? We wouldn't remove the whole apron just the excess material on top.

An alternative would be to cover the chime and some of the apron with a water resistant material such as this here: [URL unfurl="true"]https://www.belzona.com/en/focus/storage_tanks.aspx[/url]

This wouldnt improve drainage but should prevent water form accumulating underneath the tank annular plates. We are in a region with frequent rains, meaning puddles would be left quite some time atop the material. What is your experience regarding the expected lifetime and sealing capability of something like that? Most vendors show applications where they attach the material to concrete, not asphalt. Any experience with asphalt?

Thank you for your opinion on this.

Kind regards

 

[HTURKAK]

https://www.belzona.com/en/focus/storage_tanks.aspx[/URL]

This wouldnt improve drainage but should prevent water form accumulating underneath the tank annular plates]

IMO, in this case, the proposed water resistant material ( belzona ) will not work . Moreover, it will worsen the problem since water build up under the membrane . Probably , asphalt surfacing the chime and some of the apron and providing a minimum slope to avoid ponding at chimie is better .

Will you provide some more info.( type of found. (concrete ring or gravel ), bottom slope (cone down?), some descriptive sketch and some photos showing the extent of ponding ) ??

 

[IFRs]

Slapping a temporary fix that does not address the reason for the settlement is not a good long term solution. Either fix the root cause of the settlement or jack the tank up so when it settles again over time it remains above the apron.