/diy/ - Do It Yourself

I'd go another route, half n half:

Excavate, but not more than 2m (2m generally accepted as requiring engineering, so aim for less). Then build rammed earth walls for the first floor with excavated material and whatever you need for the balance. Careful with drainage around this step.

I'd add a second storey though, so we're well out of bunker territory there. But fuck that, I don't want to sleep in a dank hole.