[Cob] Arches

[Damon Howell]

Arches are really nice. I saw a photo of an earth-sheltered house  
with two arches across the front above the windows. They were very  
wide with not much arc to them. I know this was done with concrete,  
but if I wanted to do this sort of thing with cob, how wide of an  
arch could I do? Anyone with experience or knowledge of large arches  
made of cob?
Damon