A Cable Too Long

Q: I am currently reviewing a URD circuit with a cable segment that is 6,200′ per our one-line and GIS. It is our regular #2 db [direct buried] cable. I am considering the installation of pull-boxes to break up the many long segments prior to attempting injection. What is the practical limit to TDR [time-domain reflectometer] testing? What is the practical injection limit? I assume in the best case that there at least a construction splice every 2000 feet, but there may be more that have to be replaced.