digger vs ground pounder

digger

noun
  • A tool for digging. 

  • A spade (playing card). 

  • An Australian soldier. 

  • A large piece of machinery that digs holes or trenches. 

  • One who digs. 

ground pounder

noun
  • A military soldier whose primary role is infantry or the use of ground-based materiel. 

How often have the words digger and ground pounder occurred in a corpus of books? (source: Google Ngram Viewer )