How did the dwarves possibly "dig out" gigantic hallways in the mountains to create Moria with such "primitive" technology?

Question

I've just come out from Moria with the Fellowship of the Ring. They didn't quite see or hear me, but I was hovering around there and mentally "saw" their journey through reading about it in text form.

What strikes me is how dwarves long ago, even in the context of the story, somehow were able to dig out entire gigantic mountains with numerous levels of hallways and endless paths and stairways leading all over.

This is supposed to be a "low-tech" world, albeit with magical elements, so they clearly did not have modern technology or even 18th century technology from our world to dig with. I get the idea that they were basically just hacking away at the mountains in large numbers for a long time with pickaxes, but it seems like such an insane enterprise even if you love doing that.

How is Moria so incredibly oversized? I know that they "got greedy" and wanted to "dig ever deeper", but how was this even possible with such primitive equipment? Maybe they had some kind of automation to do it in their world, probably at least some sort of explosive to create new areas and to then "fine-tune" them manually with manual labor?

I find that Tolkien likes to skip over important (to me) details about the story which start bugging me until I ask about it. He could at least have had one of the younger hobbits mention this at some point, such as:

Golly! This sure is a mighty huge place! How ever did your ancestors do it, Gimli?!

And then Gandalf could've interrupted with something like:

Alas, their digging technology got far too advanced for their own good! While neglecting other, more important matters, they kept developing their specialized machines to automate much of their work, allowing them to expand Moria both wider and deeper, much quicker... Those damned fools!

But... nope. I can't remember any such comment, and I have it in fresh memory.

So how did they do it? Is it ever explained or implied?

Answer 1

I think that perhaps a bit of Dwarven tenacity is the answer here. It is clear that Dwarves were Aulë's chosen, the strongest and the sturdiest, but also the most ingenious and stubborn for projects of great complexity:

Since they were to come in the days of the power of Melkor, Aulë made the Dwarves strong to endure. Therefore they are stone-hard, stubborn, fast in friendship and in enmity, and they suffer toil and hunger and hurt of body more hardily than all other speaking peoples; and they live long, far beyond the span of Men, yet not for ever.
_{—'Silmarillion'}

Further, Khazad-dûm's construction started quite early during the Years of the Trees and continued through that period, through the First and Second Age well into the Third Age. Khazad-dûm was also untouched by the wars which destroyed Belegost and Nogrod, giving it approximately 6,000 years of uninterrupted expansion (excluding the events where Sauron's forces destroyed Eregion).

If one considers that the Kings under the Mountain ruled Erebor for 201 + 180 years (accounting for an interregnum) and accomplished a lot, it is perhaps not inconceivable that during six millennia, the city of Khazad-dûm was developed into an unrivalled scene of wealth and power—in fact, I think that Khazad-dûm was the most successful (i.e., longest lasting) kingdom in Middle Earth of all time (Lorien, the second by my thinking has about a thousand years less to it).