"Driving the workers to the point of exhaustion"

An article, Charles Crocker managed the building of the Central Pacific Railroad, in the Examiner states:

"Progress under Crocker’s considerable energy set numerous records and the project was completed seven years ahead of schedule; however, it was accomplished by driving the workers to the point of exhaustion."

Is there any factual basis for the claim about "driving the workers to the point of exhaustion"?