Lean concrete settlement values

[Quence]

sometimes you are told to put lean concrete (without aggregate) below foundation if the rock below is not level. But won't the lean concrete itself settle causing settlement problem? How many inch does a 4 inch thick lean concrete base settle?

 

[oldestguy]

As I look at it, "Lean" means low cement content, not without coarse aggregate. Usually for filling a lot more than 4". Settlement usually not expected.