noun, noun or participle which takes 'suru', intransitive verb
piling up; accumulating; lying in piles
Describes things, especially problems or work, accumulating in large amounts. Often used with する to mean 'to pile up' or 'to mount'.
机の上に書類が山積している。
Documents are piled up on the desk.
解決すべき問題が山
Problems that need solving are mounting.