Mars Base Bidron

I have been thinking about this base as soon as I learned of the contest. The main questions I wanted to answer were: how do you protect from the martian environment (temperature shifts, radiation, winds, micrometeorites), and how do you do that with existing resources? By resources, I mostly mean water. Or to be more specific, the absolute absence of any sort of liquid binder.

The solution that made the most sense to me was putting something underground. This would provide much needed insulation from the rapidly changing environment and more than adequate protection from wind. I wasn't too sure how thick a layer of soil would be needed to protect from the radiation and meteorites, but I imagine that's simply a question of depth.

That is all nice and fine, until you think, how would you do that? Digging out cavities is difficult enough on Earth, let alone Mars. You have no real clue what is under the soil. Hitting a boulder could be the end of your day. Beyond that, any hole dug