Gad is right that a "particella" is a unit, ie a property registered as owned by one person or corporation, but I don't think most people will know what "cadastral" means. And I think you could simply leave out "unit".

I think "compulsory purchase plan" sounds better than "plan of expropriation". Expropriation can simply mean confiscation without payment, which is obviously not the case here. Presumably the tender relates to a road or similar project which involves buying up land.