I havnt read the whole thread, because I havnt the time to do so

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But my input, I believe creating cave bases should cost a whole lot more than they do. Building into a mountain would take a huge amount of work even by todays standards, let alone some random guys with pick axes!!
If you only have pick axes, maybe they should only allow you to mine a certain amount of blocks into the mountain, to get deeper you would need some heavier machinery, some supports etc.
How many people die from mining even today in this day and age?? Its a very hazardous job. Mining in Rimworld is not realistic, and that's why its too easy to build a mountain base.