Carpentry and underground building are a bit hard just make sure you do calculation properly to make sure you do not get burried alive from something collapsing
(Ive been a professional carpenter for the past 12 years going on 13)
Ive never built something of this magnitude underground but i would find myself a forum//community
online of engineer since they love solving problem even if its for free and some get a real kick out of calculating those kind of situation
Wish i could help a bit more