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# How is the Buoyancy Reduction Factor Equation derived?

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## How is the Buoyancy Reduction Factor Equation derived?

(OP)
I have seen the following equation used in multiple engineering design manuals including AWWA M45, M55, and pipeline design books going back to the 90s.

Rb = Buoyancy Reduction Factor = 1 - 0.33 * Hw / H

Hw = groundwater height above buried pipe

H = depth of soil cover above buried pie

Usually this factor is used to determine the vertical dead load pressure on a buried pipe beneath a water table as follows:

Vertical Dead Load on pipe = Rb * γ * H

γ = soil unit weight

I'm struggling to understand how the buoyancy reduction factor is derived even though it is a simple equation. Google searches don't come up with anything as the results are all on buoyancy of objects immersed in water (not where the buoyancy reduction factor equation is used).

Any help is greatly appreciated!

### RE: How is the Buoyancy Reduction Factor Equation derived?

Looks a bit empirical. If the soil weight was zero, and there was only water, you'd get zero load on the pipe, which seems odd.

Nevertheless, this seems like a geology question and might be better served in another forum. I suggest deleting this thread and reposting in forum193: Soil/Groundwater environmental engineering

TTFN (ta ta for now)
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