My heroine librarian has a fictional pile of mostly standard hardcover novels, books, etc. It is not an organized stack, it is a pile.
At what point does this either become unstable or start crushing the bottom books? It can be as wide as necessary, but I'm looking for the height at which the bottom books are still intact and usable (some day).
A magnitude of order is okay over precision measurements, because there's a variety of books, and therefore some wiggle-room.
Note: It does not have any supports (steel or shelves or anything). I will deal with how books are placed on the pile, but just imagine they're placed sloppily on the top creating a massive pile.