Somewhere in the far future, an iron mining corporation has worked an ethically questionable deal with the government in which federal prisoners are sent to the mines in chain gangs. The government has less prisoners to maintain, and the mine acquires cheap labor.
But why does the mine have a need for human labor when the mine relies mostly on automation and machines?
I'm looking for a physically demanding, routine job for the prisoners to do. Something dangerous, physically demanding, and requiring a crew of people to perform. Think along the lines of the chain gang from O Brother, Where Art Thou. However, most of physically demanding, routine labor has been automated at this point in time. So what essential role do the penal laborers play? More importantly, why haven't they been replaced by machines?
Edit: Whether they are chained together or not isn't super important, but they do need to work in a group.