[Cob] dirt bags

[Nicolás Echániz]

Hi,

I guess this is not exactly the place to ask for help, as dirtbags 
buildings are not exactly cob, but I can't think of a better place to ask.

I'm planning to build a dirtbag dome (5m diameter) and I need to know 
what would be the ideal shape (curve) for this kind of corbelled dome. 
Does anyone here have relevant information on this subject?

Thanks in advance,

Nico.