The Oxford Thesaurus An A-Z Dictionary of Synonyms - pile-up n.

1) (road) accident, smash, crash, (multiple) (rear-end) collision, Colloq smash-up: Thirty cars were involved in that pile-up on the motorway. 2) accumulation, heap, stack, mass, Colloq mountain: How will you ever get through that pile-up of work on your desk?