Here is a pic of the basement cleaned up before demoing the foundation and the 2nd pic is the basement of the first house.
It varies from locality to locality. Most of the time you need to remove all the concrete. This is the common thing for houses. Yet you get on big industrial jobs and the only requirement is you remove concrete 4 feet below the final grade most of the times. If you have something that wont drain, you need to break the concrete in the bottom so it allows the water to drain.nice work, and machine... now i gota question on a job like that will you cave the foundation walls in and than fill it or just start filling with dirt?