Maybe this is a science question and not an engineering one, but how do these structures support themselves? I’m primarily thinking of mineshaft-esque structures supported by timber. How do they carve out these structures and get the wood up there to begin with? I’m looking at buildings carved into rock walls in the mideast and I’m fascinated.
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Forces are not just distributed down but also to the sides. Rock is made of solid matter and unless the forces are so high that is break apart it can survive. It is fundamentally different from how a doorway works. What is above can handle the load on it and it do not collapse,
The shape of the ceiling is very imporant. If it is flat the forces will be a lot higher than if it is a curve. There is a reason a doorway in a wall made out of rock usually has an arch on top to distribute the force. Concrete, bricks. mortar and lot of rocks handle being compressed a lot better than being stretched out. If you have an arch all of it can be in compression.
If it is flat the material at the bottom is stretched out. Steel would be good at handling getting stretched out. So if you have a doorway in a brick wall with a flat top there will be a lintel there today often out of steel but wood and even a single block of stone can be used.
Because of how forces spread out what you support is just the material directly above the ceiling. What is higher up will have forces that spread to the side. So how much rock is above you does not really have a large effect, with a tunnel is a lot more relevant
The result is you can build tunnels with no wooden support at all. You need a curved ceiling and hard enough material so it can handle the load. If there are lots of natural cracks or produce from you blasting your way tough the rock you likely need to remove loose rocks and do some reinforcing.
In mines or tunnels today that is often done by spraying concrete and sometimes filling in rock anchors. A rock anchor is like a long strong bolt you put in a hold you drill to transfer force from the surface of the rock to deep inside the rock to keep it together. In many mines today the tunnels are sized so you can fit large machines in the they are not mans sized.
If you build a min tunnel with the size of a human the woos it a reasonable support. You do not need to put them there directly because the material will have some degree of structural integrity. Even compared sand holds itself together to some degree.
In the worst case, you might only extend it with of a plank and then support it with wool from below. If the support is a bit too long you can hammer them the last way and lift up the plank a bit. You can continue on with temporary support and then add longer beams beside them and put in permanent support besides the temporary you then remove.
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