Here "granaries" represent where Babylon stored its treasures. Alternate translation: "Raid the places where her treasures are stored" (See: [[rc://en/ta/man/jit/figs-metaphor]])
Possible meanings are 1) reduce the city to piles of rubble that look like stacks of grain or 2) stack up the plunder from the city like piles of grain. (See: [[rc://en/ta/man/jit/figs-simile]])
This idiom means to destroy something completely. See how you translated a similar phrase in [Jeremiah 25:9](../25/09.md). Alternate translation: "destroy her completely" (See: [[rc://en/ta/man/jit/figs-idiom]])