from The Century Dictionary.
- noun A digging-machine or excavator actuated by steam.
Sorry, no etymologies found.
 The "steam-navvy" is, however, making digging a machine industry.
Here Norton's Abyssinian tubes, sunk in the bed after it has been carefully worked by the steam-navvy for the rich alluvium underlying the surface, would act like pumps, and dams would form huge tanks.