...Keeping people out of Dumathoin itself and trying to control traffic...
Good Luck!
There's:
+ Four railstations (at least, probably some I'm forgetting) that connect to god knows where anymore with million breaches into natural caverns and mining branches each
+ Three big grand entrances to the underground including the one that was just built for Dale (When one of the existing ones was literally just over the hill from Dale!)
+ One underwater access point that was the old "hidden" boat launch
+ Probably 50 or more random exploratory construction tunnels that crisscross into the surrounding natural caves and older mines (At least two or three of which are "on site").
What we need to do is:
+ Seal access to the central city cavern (and it's immediate appendages) with blast doors or something.
+ Immigrants we don't trust can be part of some other section of Dumathoin. It's big enough. Really, really big enough. We couldn't fill it if we wanted to. We can just throw them in "Old Dumathoin" around the original cavern, the one with the "sagging" wooden bridge and crane, which would be a fine central point for them. The older mines there are exhausted and that cuts off two entrances as well as all but the Grand Central rail station for us in the main city cavern.
+ Forget Dale, seal the new redundant entrance. (Sorry).
Dumathoin was never meant to have surface structures. I know this, having worked under Goldminer, the guy who founded Dumathoin and put more work into it than anyone. I almost feel like it's disrespectful to have Dale, right there, with direct access to the heart of Dumathoin.
minor edit:
Also if people are going to be ripping up our power rails, we might consider just sticking with powered carts. They're not quite as fast, but charcoal is unlimited and easy (unlike gold) and they're more reliable (especially with cargo trains).