On the best arch types for underground cities [closed]

I am working on a civilization that often digs into mountains, and I am wondering what form of arch would work best to hold up all the mass from the mountain above the halls. I know many arch types exist, I am just wondering which one is the best at load bearing.

I am also wondering in general how to best deal with the mass of the rock above. But most pertinent question is for the arch.

• This seems like a question that could be solved with a rudimentary amount of basic research. Is there a specific worldbuilding issue you're trying to solve, or are you asking for a list of arches. Commented Mar 15, 2022 at 2:45
– rek
Commented Mar 15, 2022 at 3:16
• What time period are you talking about? Modern age will have a different answer to the middle ages. Commented Mar 15, 2022 at 3:58
• Any elliptical arch will do, from a semicircle/hemisphere to something much taller or wider. The wider you need a chamber or arch to be at the bottom, the narrower the arch needs to be to prevent the middle from collapsing. Commented Mar 15, 2022 at 9:34
• Agree with previous remark, you did not specify. Q: Should your arch span the entire city diameter, or are we only talking halls, roads and tunnels ? An arch e.g. part of a round tunnel will not need to bear the entire weight of the mountain above it. When your arch would span an entire city, or a very large hall, it would become a different story, it would depend on the size of the mountain and the size of your city! Please add the diameter of the building or city to your question. Commented Mar 15, 2022 at 15:50

No need of arches inside the mountains

There are many examples where spaces are dug inside the mountains. There are no arches inside. Stone surface holds itself. You need arches if you dig in mud.

Outside and inside view are shown below.

Khewra Salt Mines in Pakistan

Outside and inside view are shown below. (Picture taken from here)

• If the ceiling was higher like 3 or 4 times than the pictures, would you need some arches and pillars? Commented Mar 15, 2022 at 11:11
• Normally ceilings are not dug high because (1) there is no need (2) It takes a lot of power to dig the stone. But in Khewra Salt Mines in Pakistan, in some places, ceilings are more than 4 times high because there are deep brine ponds below. There are pillars but no special type of arches. In some places, arches have been dug in semi-circular or semi-elliptic style. See images of Khewra Salt Mines in Pakistan on Google. Commented Mar 15, 2022 at 12:09
• I would imagine that also depends on the type of rock. Commented Mar 15, 2022 at 12:12
• Yes. First example is for hard stone and second example is for pink Himalayan rock salt. For mud or soft material, you need semi-circular or semi-elliptic arches or wooden planks supported by wooden poles as used in soft coal mines. Commented Mar 15, 2022 at 12:57
• Those are kinda a lot smaller than I imagine. Those are closer to tiny, tiny mountains. I mean more like several kilometres tall.
– Zoey
Commented Mar 16, 2022 at 3:18