overburden vs tip over

overburden

verb
  • To overload or overtax. 

noun
  • A sterile stratum that lies above the stratum being investigated 

  • The rock and subsoil that lies above a mineral deposit such as a coal seam. 

tip over

verb
  • (to cause) to topple over and fall 

noun
  • An action where the goalkeeper deflects the ball over the crossbar. 

How often have the words overburden and tip over occurred in a corpus of books? (source: Google Ngram Viewer )