equivalent fluid pressure ?

[willdong]

It is so confused me about equivalent fluid pressure for retaining wall. The NCEES sample use that twice other than to use Ka. When the backfill is dry, I understand the the lateral force is a triangle, 1/2*r*H^2.

But, My question is w/ the submerged condition when water exists. The answer is 1/2*(r+62.4)*H^2.

The equation in CERM is 37.43b. Ph=rw*h+Ka(rsat*H-rw*h)=Ka*rsat*H+(1-Ka)rw*h. Which part of this equation represents the equivalent fluid pressure ?

[dk28]

say 4' from grade to water pt "m" with properties
ka1, D1 and 16' from water to base of RW. pt "n" with properties ka2,D2(Total =20')
total hoz. pressure= A(effective stress)+B(water pressure)

just above pt "m"
A=D1*ka1*4 (call this eq 1)
just below pt "m"
A=D2*ka2*4
at pt "m" water pressure is 0

at pt"n"
A= (eq 1)+16*(D2-62.4)*Ka2
B= 16*62.4

so to answer ur question the whole equation u posted seems to be the "equivalent water pressure"

[dk28]

say 4' from grade to water pt "m" with properties
ka1, D1 and 16' from water to base of RW. pt "n" with properties ka2,D2(Total =20')
total hoz. pressure= A(effective stress)+B(water pressure)

just above pt "m"
A=D1*ka1*4

just below pt "m"
A=D2*ka2*4( <-----------------call this eq 1)

at pt "m" water pressure is 0

at pt"n"
A= (eq 1)+16*(D2-62.4)*Ka2
B= 16*62.4

[willdong]

i think the correction answer is :
just above pt "m"
A=D1*ka1*4 (call this eq 1)
just below pt "m"
A=D2*ka2*4
at pt "m" water pressure is 0

at pt"n"
A= (eq 1)+16*(D2-62.4)*Ka2
B= 16*62.4
------------
however, when the NCEES gives a problem of RW. They usually give the equivalent fluid pressure other than any of the equitions above. What is the relation between the Ka equations and the equivalent fluid pressure when the water exists?

[dk28]

They usually give the equivalent fluid pressure other than any of the equitions above. What is the relation between the Ka equations and the equivalent fluid pressure when the water exists?

dont worry. they will give u the information on the test.
above water they will give u equilanet fuild pressrue.
below water they will give u gamma Saturated & Ka.
based on gamma saturated and Ka you will have to obtain the horizontal pressure. If you understand what i posted before you should have any problems.
see soil books.

[willdong]