Logs as support beams in a Earthbag cylinder home??

I have a one acre lot. I'm going to do a multi room house, made of round rooms made from earthbags. I have free access to the timber around me so I want to use logs instead of beams for my roof. However the trick here is I want to put earth on the roof. Minimum two feet thick. The logs around me very in size and I have 11 square miles of logs. My question is, how would I secure these logs to the bags and each other to make the strong enough to support the roof and dirt? I am open to flat (slanted for drainage of course) and dome look. If someone could offer pics that would be greatly appreciated. I know it can be done, but very VERY challenging!! I have no problem using metal fasinors, or brackets, nails or screws either!! I can't find anything on google! Thank you in advance.

Oehler's underground house book has the engineering for sizing the timbers.

R Scott wrote:Oehler's underground house book has the engineering for sizing the timbers.

Thank you. Greatly appreciated!!

If you fallow this blog she shares lots of experience..
She put beams across the top of the wall with a slight slope and covered it with soil. eventually it was covered with tall grass which fell over and acted as a thatch.
If you are using round pole logs You can tamp the top layer of earth bags around them to hold them in place.

After I posted the above I received her latest update. She  wrote an article about the roof for Mother Earth News.  

How to Make a Living Roof