Mine collapse, again

I don't know why they ever bothered trying to dig their way in. Drilling is much more practical.

Not really. If different compartments are blocked off it's going to take many weeks to drill to each of them if not months (if they can get to all of them or they don't bring in more drills). If the stability were there they could probably have been most of the way through with their mining. But the conditions just aren't good enough.