NCEES Problem 538

[maverickmauresmo]

Why do we use at rest pressure? What scenario would we use active pressure instead of at rest pressure?

 

[maverickmauresmo]

My understanding of using at rest pressure is when soil is completely confined and can not move. I don't see how we know to use the at rest pressure in this problem, I guess.

 

[civilized_naah]

Why do we use at rest pressure? What scenario would we use active pressure instead of at rest pressure?

When a surface does not have a 'significant' movement either away from (ACTIVE) or into (PASSIVE) a body of soil, the earth pressure may be considered to be the at rest condition. This will happen for massive structures such as bridge abutments and for walls such as basement walls, which are adequately restrained at the TOP and the BOTTOM (as opposed to cantilever walls that are restrained at the bottom, but allow a lot of movement at the free end.

 

[ebow02]

In this same problem, why is the water density added instead of subtracted from to the fluid density?