Often maps have lots of civ structures to be garrisoned. After those being destructed, in place appears a pile of indestructible rubble. That garbage blocks the passage for units, yet the only way to get rid of it is to start constructing something super-close to the rubble - somehow scaffold erases those leftovers.
Just like anything in Generals civ structures ought to have same INI parameters, but i fail to find where those rubbles are created. At best i'd wish them either not created at all, or self-destruct after some time.
May somebody know how/where proper code parts are?

Sorry for the late reply, and I also don't have the game installed atm.
But have you looked into the buildings' w3d model behavior or if it has any object creation when destoryed?
I'm not sure, but you might find something useful there.

---