Should I put a retaining wall under deck/extension?

I'm unsure what my options are with my deck/house extension (see attached photos). The rock/cement posts appear to be more and more exposed each year. Would adding some kind of retaining wall between the posts and adding soil help? Not sure what kind of labor/material costs I'm looking at. I honestly don't know much about this stuff so please, any suggestions are most appreciated.

Attached Images