Gary,
Over on the C S X ( C & O, Chessie , L & N, etc, etc) we called that a ballast broom, and it would sweep the ties of ballast and force it from the top of the ties to between the cribs after the ballast regulator smoothed the shoulders and centers. We had to stay 150’ or so back to keep from being pelted with ballast. Noisy things when running with the ballast banging inside the rotary broom shroud.
STE