bank up vs pile up

bank up

verb
  • To press a mound of something against something else. 

  • To make a mound to guard against something. 

pile up

verb
  • To form a pile, stack, or heap. 

  • To collect or accumulate, as a backlog. 

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