Trivial question about Bullet and prefractured Geometry


Hi all, this is a totally basic question: I have pre-fractured Geometry and want to set up a bullet sim in Maya. Whenever I run the simpulation the parts push each other away immediately causing the geometry to fly all over the place. Split impuls makes the problem les pronounced, but still: Pieces move into all directions as they push each other away.
There has to be a way to have pre-fractured geometry (in our case voronoi fractures from Houdini) rest in place and only be pulled down by gravity for example, so: any help is greatly appreciated.