I wonder, my Kepler Bb world has a lot of different biomes. Go x regions in a certain direction and there will be a different biome.
Region 1, where the first city is, has a river, lakes both isolated and non isolated, a cave, a mountain range, forests, and grasslands.
Region 2 is similar but there are fewer forests and the lake there is a crater lake. There once was a huge mountain there but a significant part of it got knocked off by an asteroid and this lake is what is left of it.
Region 3 is swamp throughout.
Anyway, there are 2 biomes where the people that live underground would have to dig through sand. 1 of those is beach at the coastline or in very rare cases, inland. The other one is a hot, sandy, desert.
In both cases, there is a problem, sand is so fine it would most likely collapse if a humanoid tried to dig a tunnel in the sand. But then again, there are quite a few creatures that dig holes in the sand in both of these biomes.
But does this mean that sand wouldn't collapse?
Because here is what I think would happen. At first digging down goes really well but then the humanoid starts to go in directions other than down and what happens? As these more horizontal tunnels are dug, the sand up above puts so much weight on the tunnel that it collapses and the humanoid, quite literally, aspirates the sand as he/she digs back up to the surface. A lot of sneezing and coughing and a desperate need for water results from all the sand the humanoid gets in its nose, throat, and lungs. While dust will just give a person aspiration pneumonia and/or sneezing without a scratchy throat, sand would give the humanoid the same thing but with a scratchy throat.
That is not good. Sand is so fine and so vulnerable to collapse. How would a humanoid dig tunnels through the sand without the sand collapsing on itself? Wet sand probably would not cut it. In fact, at just the right ratio, the wet sand becomes quicksand which itself has its dangers since you can get stuck in it.
So they would have to use something other than sand to keep the tunnels from collapsing. The only thing I can think of them doing here is putting rocks all around the tunnels and sticking them together with mud or something that wont crumble into fine pieces as soon as it dries(which I think wet sand would do).
They are at stone age level technology. This means that they build everything from hunting weapons to homes and everything in between without using metal. The closest they have to metal is stone.
Is there anything else they could do to keep tunnels in sand from collapsing?