EFP on retaining wall

[DavidStructural08]

For example, a wall of 12' high retaning a soil of same height, but a limited width, say 6'.

the question is:

what is the EFP on the wall? Is it different than the one for a wall retaining a 100' wide soil?


wall 12' high-->|xxxxxxx|<--wall 12' high
^
soil 6' wide

 

[DavidStructural08]

ok. My question is really this:

are the EFP's different on retaining walls which support 6' wide soil and 100' wide one?

 

[civilperson]

What is a "EFP"?

 

[DavidStructural08]

equivalent fluid pressure

 

[MiketheEngineer]

Well it can't be more then 6' - maybe only half that assuming the "open" side of the fill is not retained in any way.

 

[kslee1000]

Answer your question: NO.

 

[DavidStructural08]

ok guys. I am confused. Please educate me:

Say the equivalent fluid pressure is 65 psf/ft for a natural soil.

Q1: What is the equivalent fluid pressure from a 1' wide soil, which is retained on both sides by the walls?

Q2: What is the equivalent fluid pressure from a 6' wide soil, which is retained on both sides by the walls?

Q3: What is the equivalent fluid pressure from a 100' wide soil, which is retained on both sides by the walls?

 

[kslee1000]

Equivalent Fluid Pressure acting the same way, as the word suggests, as "FLUID" - water, or any flowable material. The result is applied to an unit width - 1'. Please review fluid mechanics or soil mechanics text books.

 

[KBVT]

It is the same, what is the fluid pressure of at the bottom of a 12" tall cylinder and a 12" tall swimming pool. The same.

 

[WillisV]

I believe you are asking how can the pressure be the same from 1' of soil to the side of the wall face as opposed to 100' given that the plain of soil failure must extend at some angle from the base of the wall up to the surface of the soil (with some exceptions in soil types) - so if that failure plain is not contained fully within the soil (e.g. if only 4' of soil width is retained by a 20' tall wall), what is the pressure?

There is a journal article: "Earth Pressure on Retaining Walls Near Rock Faces"
Sam Frydman and Israel Keissar, Journal of Geotechnical Engineering, ASCE, June 1987, Vol 113, No. 6

That discusses a similiar issue and concludes that you can use smaller active pressures in these situations for well drained soils because the full soil wedge can't be activated.

 

[DavidStructural08]

kslee1000,

so if the equivalent fluid pressures are the same, the forces the wall will retain are the same, no matter what the volume of the soil is?

In other words, 1" soil will put same amount of force on wall as 100' soil?

Maybe I did not say clearly, by saying "1" or "100'" wide soil, I mean the section width.

 

[DavidStructural08]

thanks WillisV. What you said is exactly what I wanted to ask.

 

[kslee1000]

Sorry, didn't read through your question correctly before jumping to provide answers.

WillsV is correct. I remember years ago I had similar discussion with one of my senior associate, the conclusion was that the "Wedge Method" was the proper way to go to determine the soil pressure for such case. I believe US Corps of Engineers has guildlines on retaining walls containing shallow soil body behind the walls. You may want to check it out.

 

[miecz]

See thread255-232396.

 

[civilperson]

Width of wall vs. amount of distance of soil behind wall:
The pressure is the same at equal elevations for differing widths of walls. The pressure may be lower if less than sufficient soil is behind wall for the failure plane to intersect the surface.

 

[hokie66]

Just goes to show that words like width, depth, length have different meanings to different people. Lack of clarity of statement of the question caused several people to waste their time.

 

[kslee1000]

One picture/sketch better is than thousand words. However, an experienced engineer shall refrain from jumping into conclusion before having full understanding of the questions and backgrounds.