AutoCAD Civil 3D

[#1]

I tried the RetainWallToLowSide subassembly and ran it through the corridor, but I'm still having trouble burying the bottom of the wall deep enough below the design profile. 

I have attached another image illustrating an example of a problem area at a station along the alignment. As you can see, the bottom of the retaining wall isn't deep enough and protrudes out of the slope. I want it to be buried deep enough so that there exists the 5' horizontal cover from the bottom of the wall outwards.

[#2]

It got flipped on you because you went into a little bit of Cut on that side.  You could use a Conditional Cut/Fill on that side  and control the Side parameter for this wall Subassembly on this steep slope side. If you flip the Side parameter and specify an appropriate Footing Cover everything should look reasonable.

If you really want that 5' offset footing cover/depth, I think you're going to have to go SAC on it, because the footing cover for this SA will not  take an elevation.