AREA SURCHARGE AND EFP

[kkoloj]

Using EFP, for an area surcharge load (i.e., a load of infinite length and width) behind a retaining wall, wouldn't the magnitude of the force be S x H (where S is the surcharge load in psf and H the wall height in ft)? Wouldn't the magnitude of the loading diagram be S? And thus the moment be (S x H^2)/2?

Thanks in advance.

 

[DRC1]

I'm not sure what "EFP" stands for, but for a wall with an infinite surcharge S, height H,and coeffient of lateral earth pressure k, the magnatude of the force from the surcharge would be S x k x H and act at H/2.
k can be active or at rest pressure (usually passive is not used in retaining wall design)
The retaining wall will also see lateral load from the soil and groundwater which will need to be added to the surcharge load.

 

[BigH]

I've never ever used EFP in nearly 30 years of writing reports. Conduto, I believe, has a section on EFP (it took me about 2 mintues to figure out the acronym too).

 

[DRC1]

If EFP means equivilent fluid pressure, then I would like to clarify my post. An equivlent fluid loading is linearly increasing (trangular). The loading diagram for an infinite load surchrge is a uniform pressure yielding a rectangular shape.
Note that if the surcharge area is large enough, this may be a good approximation. However if the surcharge area is localized, the shape will be parabolic.

 

[emmgjld]

I present EFP information as long as the problem is simple and the retaining structure is not large. I usually limit the use to retained soil less than 10 to 12 feet and very simple loading conditions. As DRC1 notes, Surcharges which are point loads, concentrated or not uniform require better methods of analysis.

 

[kkoloj]

Thanks everyone for the responses.

Maybe it wasn't such a good question. But as "yack" pointed out, most soils reports that I have read provide EFP values for designing retaining walls (of course, at the back of these reports there are shear strength tests which provide phi, which can be used for Rankine, etc.). Therefore, if one is trying to determine the moment from an area surcharge (infinite length and width) using an EFP approach, what is the load diagram (and thus the moment) behind the wall.

 

[Focht3]

You still need to evaluate the surcharge independently, then add the pressure distribution to the back of the wall. Don't try to use an equivalent fluid approach for surcharges - it's not appropriate for most problems.



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"