Seismic Force for a gravity wall in AASHTO

[Awre]

Hi,

I posted this in the Earth Retention Engineering forum, but I had no luck for three days.
I am calculating the seismic force on a gravity wall per AASHTO.
The concentrated dead load surcharge pressure distribution is not clear (to me!).
How can I estimate the maximum, and minimum pressure values for the trapezoid to calculate F_p?
Also, is K_af is the same as K_a utilizing Coulomb, etc.? or is it different? I do not see how Kaf is calculated...

Lastly, does the diagram imply that only dead weight to be considered, and no live loads etc?

I am attaching the figure from AASHTO... I appreciate any help... Thanks

 

[bones206]

I believe the notation K_af is referring to active earth pressure of the backfill. So standard methods apply, the "f" is just referring to the fill specifically.

 

[Awre]

Thanks!

Any idea on the surcharge load calculation part?... Thanks again

 

[bones206]

What aspect of the surcharge load are you trying to figure out?

 

[Awre]

Hi bones206!
I need to figure out the trapezoidal load distribution for the surcharge load, which is shown in the attached figure of my original post.
It appears that the maximum at the surface is: K_h*W_surcharge, correct?
What is the minimum at the toe of the wall?
And how to calculate the F_p, and W_surcharge
Also, are k_h and k_af the same? Thanks