# PPE Exam Cafe Prob. 18 PM Construction



## brbowhunter (Oct 8, 2010)

Anyone else work this one? I get 320 lb/ft. They're solution does not make sense to me...

Problem 18: Construction [E0304090022]

A cross section of a concrete cantilever retaining wall is shown. The foundation sand, located below the base of the wall and in front of and over the toe, has a unit weight of 120 lbf/ft3 and a friction angle of 30°. The backfill sand, placed behind the wall and over the heel, has a unit weight of 125 lbf/ft3 and a friction angle of 34°. The water table is a considerable distance below the base of the wall and the backfill is well drained. Both sands are cohesionless. The base of the wall is 2 ft thick and 11 ft long, consisting of a 6 ft heel, a 3 ft toe, and 2 ft under the stem of the wall. What is most nearly the horizontal passive (resisting) earth pressure acting on plane BB′ per foot of wall?

720 lbf/ft

850 lbf/ft

2900 lbf/ft

3400 lbf/ft

Solution:

First find the passive earth pressure coefficient for the material at the toe.

Now find the passive earth force.

The answer is C.


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## Ambrug20 (Oct 8, 2010)

brbowhunter said:


> Anyone else work this one? I get 320 lb/ft. They're solution does not make sense to me...
> Problem 18: Construction [E0304090022]
> 
> A cross section of a concrete cantilever retaining wall is shown. The foundation sand, located below the base of the wall and in front of and over the toe, has a unit weight of 120 lbf/ft3 and a friction angle of 30°. The backfill sand, placed behind the wall and over the heel, has a unit weight of 125 lbf/ft3 and a friction angle of 34°. The water table is a considerable distance below the base of the wall and the backfill is well drained. Both sands are cohesionless. The base of the wall is 2 ft thick and 11 ft long, consisting of a 6 ft heel, a 3 ft toe, and 2 ft under the stem of the wall. What is most nearly the horizontal passive (resisting) earth pressure acting on plane BB′ per foot of wall?
> ...


I remember working this problem. I think its erra there. They said to find Kp (passive coef), but did calculate active coef.- Ka.


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## brbowhunter (Oct 8, 2010)

Tanya said:


> brbowhunter said:
> 
> 
> > Anyone else work this one? I get 320 lb/ft. They're solution does not make sense to me...
> ...


Great Just wanted to make sure....


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