After you move the two trash carts (see other threads) you end up in an area where you can access the top level of the trash compactor room. Just before you reach the door to this top area there is a short ramped area with gray walls where some three eyed guys attack you. there is a grate on the wall here. Smash it and jump in and look down. Blow up the explosive crate. You can now go back down and go through the new hole.
You'll be meeting old smoothy soon enough.