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# Equivalent Fluid Pressure2

## Equivalent Fluid Pressure

(OP)
In all of the responses addressing EFP, I have seen that al of the descriptions always seem to refer to finding the Equivalent Fluid Pressure based on a value given in a geotechnical report. My question is where does that value in the report come from and how is it generated? If the report says "use 60 pcf" for the EFP, how was that value calculated?

### RE: Equivalent Fluid Pressure

We usually use the Rankine equations.

If  you look up on Google the name Rankine, you may get some info that is not related to lateral earth pressure, but try this link.

Rankine seems to have been very busy figuring out formulas for many engineering subjects.

http://www.uwplatt.edu/~meyersm/wetzel/ce473ch5/ch5a.htm

Also, check out the lateral earth pressure info from the work of Peck in Chicago.  It is not always an triangular distribution.

### RE: Equivalent Fluid Pressure

2
I'd like to see us drop the use of "equivalent fluid pressure," and do something more fundamentally grounded in soil mechanics, such as active pressure (based on bouyant unit weight plus hydrostatic pressure below the WT).  We're not dealing with a fluid, and the results don't always fit the model of "equivalent fluid pressure."  Soil is a solid that exerts a pressure that depends on placement/compaction and wall stiffness.  Pressures change with changes in the water table.

It ain't hard - you all did it as undergrads.

DRG

### RE: Equivalent Fluid Pressure

(OP)
I agree with dgillette's suggestion that we do away with Equivalent Fluid Pressure. I have several recent editions of certain geotechnical engineering text books, and not a single one of them even mentions "Equivalent Fluid Pressure". The soil mechanics equations and procedures seem to have been worked out without "Divine Inspiration" to come up with a nefarious number in a project geatech report.

### RE: Equivalent Fluid Pressure

Amen, DRG.  A lot of young engineers think earth pressures are like water, and don't seem to understand that they can be greater than hydrostatic.

### RE: Equivalent Fluid Pressure

. . . and not triangular!

### RE: Equivalent Fluid Pressure

However, when will structural engineers gladly accept the  more "complicated" pressure distributions?  In my experience, the simpler it is, the more they go for it. In some cases, even when very simply stated, they don't understand it.

That usually seems to come about when a long, very detailed geotech report is written and the meat of what is needed is buried in a long bunch of words.

In retrospect, when has the use of EFP caused a failure?

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