hi phil
i just wanted to say hi and say i understand what you are looking to do and if you need help in the future i am right in your back yard willing to help just for the fun of it
some problems i can see just looking for someone only doing allot of study on the subject of cob would be how much humidity we have hear could be a problem being underground there are others hear in nashville area that are building with cob (might be a good group to contact about how cob in that form would work in this area) they are in the permies site might want to look for them and contact them i can see a possible problem with cob working the way it should with needing to breath
is it strong enough ? might be the way it bind togeather from what i can see how the staw holds it all togeather its very strong but the problem there could be the undergroud factor again if it got wet in any way it would basicly turn back to mud and would fall back onto itself
maybe and i only say maybe as a infill with a strong frame to hold it all up could the cob hold up would be my guess
i would say you would have to be 100% possitive no moisture would ever get to it
now all of this info is from someone only doing allot of study on the subject no real world experiance at all
i know for a fact because others have built cob home's in our area and are living in them that it can be done above ground with a great hat (roof) and shoes (foundation)
please keep talking about it with others i would be very interested about more info on this subject and have been looking for other wanting to build in a natural way like this would for sure love to help eather way and make a connection with someone for when i am looking to build something in a natural way like this also i am looking for land to start with so when i get to that point i will be building something most likely cob infill something along that line
hope the best on your path to hobbiton may your doors be round and your feet large
ken