unworkable       
adjective uk/ʌnˈwɜː.kə.bəl/ us/ʌnˈwɝː.kə.bəl/
 (计划)不可行的,难以实施的
An unworkable plan is not practical or cannot really be done successfully.
  To be honest, I think the plan is completely unworkable. 老实说,我认为这个计划完全行不通。 
 Synonyms: impracticableinfeasible unfeasible
Opposites: feasiblepracticable viableworkable (HAVING EFFECT)