load combination for hydrostatic uplif
 

load combination for hydrostatic uplift
i have a 20' deep concrete tank, buried 15' into the ground.
flood elevation is 3' above the ground (non-coastal a-zone), what load would be used for determining bouyancy for the tank?
asce 7-05 2.2 defines h as "load due to lateral earth pressure ,fff"> ground water pressure or pressure of bulk materials(note the comma)." so maybe the bouyancy force is h.
however the commentary suggests h is due to lateralfff"> pressure due to soil andfff"> water in soil..". the bouyancy force is not lateral, so maybe it is not h, but actually fa (flood load). there's a big difference in the load factor (1.6 vs. 1.0)!
what if it is just ground water and not flood water??? back to h? f (fluid load) doesn't see appropriate...
any opinions out there?

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yes, ignore asce7 for buoyancy.
i think it is technically hydrostatic (h) load....see asce 7-05, section 3.2.2. also, the commentary for c2.3.2 seems to imply that f loads are more about tanks and not earth/bouyancy issues. althought, this commentary also mentions h loads as lateral - with no reference to buoyancy.

due to uncertainties, hydrostatic uplift is usually treated as a live load event.
jkw05 seems to be referencing fa (not f) in 2.3.3, 2.4.2 and chapter 5. for non-coastal zone a, the asd combination 7 becomes 0.6d + w + h + 0.75fa. is the sub surface water pressure counted twice, once as groundwater pressure (h) and once as flood load (0.75fa)?