PPE Exam Cafe Prob. 18 PM Construction

[brbowhunter]

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.

 

[Ambrug20]

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.

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

 

[brbowhunter]

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.

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

Great Just wanted to make sure....