1.
If you pile up a quantity of things or if they pile up , they gradually form a pile.
Bulldozers piled up huge mounds of dirt...
Mail was still piling up at the office.
PHRASAL VERB : V P n (not pron) , V P
2.
If you pile up work, problems, or losses or if they pile up , you get more and more of them.
Problems were piling up at work...
He piled up huge debts.
PHRASAL VERB : V P , V P n (not pron)