Hi guys, I've had similar thoughts of finding a way to combine a earth bermed back wall with cob construction. It would be cool to have a vent that ran through the berm and looped back into the house for a passive a/c system.
My idea was to build the foundation up, timber frame the roof, then build up your cobwalls in that then created dry space, maybe use a different material for the back wall where the berm comes in if necessary.
THEN when you bring the earth berm in use dry dirt and throw a giant pond liner over the whole structure including the berm. Bury it one more time and grow some herbs.
What do ya think?