im tracked problem and solved stuck issue
its because
if you want to push a func_pushable you need a empty space atleast one player can fit inside, you cant walk in that tiny space so pushable brush cant move either..
I made a 36 units empty space (4 unit added to your empty space of walls) so pushable can be pushed
picture:
http://u1309.hizliresim.com/1f/9/sgu2t.jpgalso you should know triggers can be triggered by pushables.
you can solve "one way movement" that way, just think about it..
for example make a func train behind the pushable brush,
(func train will be act as a "pushable brush holder" in this example)
when you move pushable brush, it will activate a trigger somewhere forward.
trigger will send message to func train and it will move a little.
maybe it will push forward the pushable brush too.
when func train will reach path_corner, it will stop and gonna wait for next trigger activation.
make another trigger and continue this chain reaction..
pushable brush cant go back because there is a barrier behind..
have a nice mapping