what is the minimum requirement in inches for direct burial UF cable...

[Dusty]

...installed outdoors that supplies power? for a 120V, 30A circuit

 

[MreWormDoodle]

Depends on type of location:
In soil where there is only pedestrian traffic--24"
Under 2' of concrete --18"
Under streets, driveways, parking lots--24"
Under residential driveways--18"