jyf
Having personally worked in Alberta, someone building a 'sedimentation' pond with a clay liner, at 1:1 slope seems to me like a fantasy scheme.
It sounds like a evaporation pond is likely what you are attempting to design. In that case, a clay liner built on a 3:1 slope at 95% standard...
Theres no question that a slab can take some of the load. I always like the what if game. What if later on someone removes the slab? Is it permenent with the life of the wall? With that in mind I'm with fattad, if you can't count on on it then lower the base and design for passive soil pressures.
I wouldn't suggest that you use the angle attainable by a pile of crushed rock to be the friction angle. It would be closer to 45 + phi/2 (where phi is friction angle and is also dependent on the relative density).
