This morning I found by chance this very interesting website (well, it is interesting if you like wind farm constructions…).
Basically it is an Australian company using “rock slingers” (that is, conveyors belts connected to a dumper) to backfill trenches mounted on small vehicles (2.5 meters wide). The equipment is made by CAS, an American company specialized in this kind of equipment.
It is a remotely controlled machine that can create the sandbed inside the trench accurately and at a great speed. According to the figures provided in the website the slinger can create 16 Km of bedding in a day, using up to 1000 tonnes of material.
I guess that they call it "slinger" because it can throw material at a quite remarkable distance (over 40 meters). Used in combination with one or two trencher it looks like it can lead to relevant savings, less labor and a more homogeneous distribution of the material.