Question updated based on the "on hold" vote...

Assuming we're on Earth (or something geologically and biologically comparable). Humans are at best in the middle ages, and there's no "magic" or advanced science.

Now the difference is, there is also a "Dwarf" species (presumably just some "Humans" that split off from the main branch a few thousand years ago). They don't like living on the surface, for whatever reason (could be as simple as "religion", for example). So they live underground, but presumably have shafts to the surface at regular distances (for fresh air, commerce with Humans, ...) Dwarves have a similar technological level to Humans, but are more advanced in dwarven skills like mining and forging...

So the question is: since Dwarves need to mine to "open up space" to allow their population to expand (and to gain resources, obviously), how do they get rid of all that stone? They would have so much of the stuff that it's basically a waste product. They have many options; they could drop it into "sinkholes" (if they happen to find one), or drag it to the surface and just dump it there, or use it to do commerce with the Humans, or build fortifications and infrastructure on the surface...

Which of those options would they favor best (and why), from a traditional fantasy dwarvish point-of-view? It should ideally take into consideration Dwarve's "values", and their strong technical and logistics abilities.

For example, Dwarves are traditionally "xenophobic"; they might deal with a few select Human traders that come to them, but they would probably not drive around in carts, selling their ware directly in the Human markets. OTOH, they probably would accept (large) orders from the local Human nobility, as refusing could make their life more difficult.