I wonder if the carbon released by digging holes and cutting down the bamboo is greater than the carbon sequestered this way? At any rate I'd suggest not bothering to bury the bamboo, you can just pile it up somewhere.
Well, we have all sorts of schemes proposed to partly burn biomass and bury or spread the resulting charcoal. Surely raw green bamboo would hold more carbon.
Bamboo rots and emits methane.
Yeah, you'd have to bury it deep enough to prevent decomposition within a few hundred years. Holes that big are hard to do without heavy machinery which guzzle fossil fuels.
I wonder if you can sink the bamboo in the sea?
It's easy enough to secure big rocks to bamboo, but the same problem arises, how do you get tons and tons of bamboo and any required ballast out to deep water positions? Cargo ships! Which are some of the worst polluters on earth.