They are generally economical up to 10 feet in height for cast concrete structures.
Poured concrete retaining wall height.
Concrete retaining wall footing size the depth to the bottom of the base slab should be kept at a minimum of two feet.
In general the top of the stem of any cast concrete retaining wall should not be less than 12 inches for the proper placement of concrete.
Taller walls backfilled with heavier soil risk failure unless correct design methods are followed.
Recommendations there are some basic rules of thumb for foundation wall thickness and these are outlined in many modern building codes.
Poured concrete foundation walls that are less than 8 feet tall and have soil outside that is 6 or 7 feet deep against the wall can often be 8 inches thick and function quite well.