Attached is a calc for load on segmental wall. It is not slightly "liberal" as I try to account for all factors that will help resist sliding and overturning. There is essentially 3 parts.
There are 2 types of walls: Walls that are taller than the foundation and walls that are shorter than the foundation (short walls).
For walls taller than the foundation I consider 2 parts:
Part 1 overall stability. Just add the force on the fence or rail to the your overall sliding and OT calcs.
Part 2 is local stability. Here I use the weight of the units, geogrid, and passive soil between units. However I do not use the weight of the foundation, I am considering using the weight of the foundation and removing the passive soil between units. I distribute the force from the foundation at a 45degree in plane view to the back of the wall and also vertically down through the wall for the height of the foundation.
If you go through the calc let me know your questions/comments.
Short wall calc uses same factors as Local stability but also includes passive soil below retaining wall.
Thanks
EIT