Seismic and Soil loading

[bbartlet]

I am designing a 2-story building that is retaining soil on one side and I am trying to determine the greatest load combination to the shearwalls.

The wind load into the floor diaphragm is just slightly greater than the seismic load into the floor diaphragm at the 2nd floor level (neglecting soil load up to this point).

My question is, do I take a percentage (Cs, as determined from ASCE-05 Section 12.8) of the weight of the soil being retained and add that to the load from the floor and if so will this be acting in conjunction with an active pressure soil load?

If this is not the case, then the wind load will control.

 

[kslee1000]

What I would do is to fix the building columns at the building-basement interface, assuming the worst case scenario - the buildings and the basement move in opposite directions. This shall clarify the governing case.