Retaining Wall - Active Height Calculation

Comparing how two different authors do active height... Which one is correct?

In the CERM (14th edition page 54-5, example 54.1), the active height is taken as the height of the soil retained plus the depth of the base (19'+2').

In Michael Frolov's Civil PE Exam Success (Problem 3), the active height is taken as only the height of the soil retained, NOT including the depth of the base (8.7m). Running the calculation both ways (with and without), gives the same answer since the available choices are spread out.

Can anyone shed some light on which is correct?

The first approach is right. The only instance where you would use only the height of the stem is if you were trying to calculate the maximum moment in the stem (to figure out required reinforcement etc.)

Civilized - Thank you for the clarification!

I agree with civilized_naah. Usually you assume all the way to the bottom of the ftg when you check overturning, sliding, bearing for the overall assembly and reinforcement in the footing. Sometimes if you have a key some authors extend the active pressure all the way to the bottom of the key which makes it worse.