Buoyancy Pressure under tank 1

[adk48ist]

Will someone tell me whether the buoyancy force increase with depth. I have a precast concrete tank where top of concrete is 3' below surface and the water table is at grade. the Tank is 9 feet deep and covers an area of 10'x80'. I calculate the buoyancy (uplift force) as 10'x80'x9'x62.4pcf=449280lbs. Is this correct? That is the weight of displaced water mass. The fact that the top of tank is 3 feet under the water table doesn't play a role here. THe buoyancy is not dependent on the depth?? So regardless hhow deep in water the tank is buried the buoyancy force is the same. Can someone confirm or challenge this please; I must have failed My physics 101.
thanks

 

[PEinc]

The upward force on an immersed object is equal to the weight of the displaced fluid. (Civil Engineering Review Manual, 3rd Edition, Michael R. Lindeburg, P.E., page 3-14)

Don't forget that the uplift force is resisted or partially resisted by the weight of the structure.

 

[Cosimo]

An off shoot of the same question...... When calculating anti-flotation, is the submerged unit weight of soil always utilized?

 

[CarlB]

Yes, use the buoyant unit weight for soils below the water table.

 

[DRC1]

Since the fluid is hydrostatic,the upper three feet exerts a counteracting downward force so the net force (bouancy is only a function of the six foot ht not thje 9 feet. Which means it would have the same bouancy no matter how deep (until the water table dropped be low the top of the cover. This aslo assumes the cover is tight and the box is dry.