Retaining Wall

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prob_1.pdf
Why "B" is not the correct answear?.....I'm getting 1,767 lb/ft
Sorry, this is the problem
I am getting:

K_a = 0.28 (for phi = 32, delta = 16, beta = 0, theta = 90)

R_a = 1610 lb/ft

R_ah = 1550 lb/ft

Answer (A)
You are right. correct answear is A).

now if the total weight of the wall is equal to 100 kips and the the problem ask to calculate sliding force the result will be S=28.7 kips...am I right?

 

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now if the total weight of the wall is equal to 100 kips and the the problem ask to calculate sliding force the result will be S=28.7 kips...am I right?
No, the sliding force is R_ah. What do you mean by TOTAL weight of the wall = 100 kips? That's not per foot (width) right? The frictional resistance will be total weight (wall + soil) times the friction coefficient. Assuming the fricton angle UNDER the wall footing to be also 16 degrees, the friction coefficient = tan 16 = 0.287. I assume you mean 100 x 0.287 = 28.7 kips. But that's the RESISTANCE to sliding, not the force CAUSING sliding.

 
now if the total weight of the wall is equal to 100 kips and the the problem ask to calculate sliding force the result will be S=28.7 kips...am I right?
No, the sliding force is R_ah. What do you mean by TOTAL weight of the wall = 100 kips? That's not per foot (width) right? The frictional resistance will be total weight (wall + soil) times the friction coefficient. Assuming the fricton angle UNDER the wall footing to be also 16 degrees, the friction coefficient = tan 16 = 0.287. I assume you mean 100 x 0.287 = 28.7 kips. But that's the RESISTANCE to sliding, not the force CAUSING sliding.
yes, that's what I referred to"Resisting to Sliding"

thanks civilized, I will correct a principle that I got wrong!

 
I'm a little confused on this, can someone explain...

I seem to remember this same question coming up somewhere else on here where the general consensus was that answer B is correct.

I know that you get answer A using the long form of the Ka (active lateral earth press. coef.) , and that you get answer B using the shortened Rankine Ka.

The problem doesnt say "using the Rankine Method" so wouldnt using the long Ka equation be correct, therefor making A the correct answer?

 
I take back what I posted

 
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