I stand by my argument, for if that's the purpose, the means are all wrong. In terms of pain, dying under five minutes from suffocating is nothing compared to a slow and agonising process of dying from hunger while being buried. A process which can last up to a month or so, assuming we will water him regularly so he won't have the possibility of choosing the quicker route of death by dehydration. Not only will it be a mix of pain coming from his insides demanding feed and the not too pleasant fact of being immobilized completely (additional points if the victim is claustrophobic), it will also destroy his mind, for at the beginning he will be aware of the demise that awaits him, knowing that he can do exactly nothing to save himself, which will eventually break him in one way or another, while at the later stages the unimaginable hunger will make his awereness disappear, turn him into not much more than a brain-hungry zombie at best and shred the already weakened mind to pieces. Just imagine all that fun, plus the eventual longed-for demise of a dehumanized unit, of course.