stack up vs upheap

stack up

verb
  • to pile up; to accumulate. 

  • To put a group of abstract things together. 

  • To put into a stack. 

  • Often followed by against or among: to compare with (something); to measure up. 

upheap

verb
  • To pile or heap up; accumulate. 

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