  A tropical expansion is a degeneration of a toroidal embedding induced by a
polyhedral subdivision of its tropicalisation. Each irreducible component of a
tropical expansion admits a collapsing map down to a stratum of the original
variety. We study the relative geometry of this map. We give a necessary and
sufficient polyhedral criterion for the map to have the structure of a toric
variety bundle, and prove that this structure always exists over the interior
of the codomain. We give examples demonstrating that this is the strongest
statement one can hope for in general. In addition, we provide a combinatorial
recipe for constructing the toric variety bundle as a fibrewise GIT quotient of
an explicit split vector bundle. Our proofs make systematic use of Artin fans
as a language for globalising local toric models.
