pile up, cram in

積む(つむ)	To pile up things (luggage, cargo, crap) or, to accumulate. Almost always used like this:積み上げる.

積上げる(つみあげる)	Pile up.

重ねる(かさねる)	To overlap (usually said of flat things). Also, mostly it is used in the figurative sense:problems or responsibilities are growing out of control, you can’t do it all at once!

詰める(つめる)	To pack in, stuff in, cram.