pile up in WordNet English dictionary

1. collect or gather
   "Journals are accumulating in my office"; "The work keeps piling up"
   accumulate  cumulate  conglomerate  pile up  gather  amass 
   
2. get or gather together
   "I am accumulating evidence for the man's unfaithfulness to his wife"; "She is amassing a lot of data for her thesis"; "She rolled up a small fortune"
   roll up  collect  accumulate  pile up  amass  compile  hoard 
   
3. arrange into piles or stacks
   "She piled up her books in my living room"
   pile up  heap up  stack up 
   

pile up in English Wiktionary