exported meshes to .OBJ from Silo are melted in Blender

Hi all

im very new to blender, but since this is a very powerful player for working with unity i choosed Blender.
Well my question ist sure very simple.

Since i love Silo for Polymodelling im made a bit of a mockup of a level i want to texture in Blender an make the elements ready for Unity.

here in Silo:

But when i open my .OBJ in blender my streets are merged to one (See outliner . Cube.001):

I never saw this before when using obj, can someone give me a tip about this.

Im using newest Blender on osx.

thx for your help