pile-up vs stacks on the mill

pile-up

noun
  • A pile of tackling players. 

  • An accumulation that occurs over time, especially one which is not welcome. 

  • A pile of crashed vehicles due to a traffic accident. 

stacks on the mill

noun
  • Synonym of dogpile, especially in Australian football. 

  • A children's dogpile game. 

How often have the words pile-up and stacks on the mill occurred in a corpus of books? (source: Google Ngram Viewer )