If we want to construct a road in desert at least 2 meter high & A-4 or any other clay material is also not available for confinement,what technique ?

I think that you should deal with nature by using sand located to reach the level bridge proper, no more than1 meter by3-4 layers , with the saturation of sand with water and a very good compaction, and then start bringing A3 or A-4, and should bethe last backfill layers  of the kind A1-b  or A1-a ,  with the knowledge that the transportation cost will be more than usual ... but I think the most appropriate solution in this case.