Peripherally related, this pyramid talk finally made me look up "critical angle of repose" of various materials: https://en.wikipedia.org/wiki/Angle_of_repose#Angle_of_repos....
The Great Pyramids are around the 50° mark, where modern wheat's angle of repose is roughly half that (27°). That's not to say a pyramid-like structure couldn't be used to store wheat—just that the shape of these particular pyramids don't directly mimic the free-standing angle that a wheat mound would form.
There is a "ski Indiana" photoshop showing a skier on one of these grain hills.
Here is a nice little pdf with a lot of ways we store product http://calculators.agstar.com/uploads/GrainStorageMethods070...
[edit: I agree they would have been a bad shape of an old style grain store, plus wrong era]
> But Stevenson also says that counter-theories about the pyramids actually being huge grain stores are not helpful. “Archaeologists have in fact found grain silos in Egypt, they’re well known to us and they look nothing like pyramids,” she says.