I had this idea for a "drill" that I'd like to make someday.

Basically it was a box with several tentacles snaking out of it. The tentacles would each have a drill on the end, and they would dig holes in a surface. These holes would be spaced apart and they would be on the outer edge of where the tunnel is meant to be. The silicon arms would be full of actuators that measured their resistance in terms of the momentum they want plus the gravity weight of any nodes after them.

After drilling around the surface, they'd turn (hence tentacles) and tunnel inward. Then, a big hammer or other impact would hit the main surface (after ensuring there were no tentacles below) and the shock of the impact would significantly reduce the amount of rock to carve through.

I really want to know why this wouldn't work, but I'm a designer, not an engineer, and I don't feel like making products. gee I sure wish I knew a bunch of engineers who would make this for me or at least tell me why it wouldn't work so I could use it sometime. Oh sorry for wanting there to be tunnels in every city on earth so we didn't have to destroy woodland to build suburban cities at such a gorgeous rate, I'm just a forest witch who doesn't fit in with startup founders and product engineers. gee wish there was a market fit for me.

"we don't have to dig through the rocks, just dig around the big ones and let them fall free" every digger knows this

I figure a big issue is you still need to move all of that displaced rock and earth out of the way

I’m having trouble picturing this, I think. Maybe this will help: after this big hammer hits the rock with the outline of drilled holes around it…where do you think the rock goes? It’s not hollow under there…