Karst caves can be dangerous for building tunnels. Scientists used special imaging techniques to find karst caves near a subway tunnel site. They discovered many caves, mostly around 5 meters tall and within 15 meters of the tunnel. By creating computer models, they found that caves closer than 7 meters to the tunnel could cause it to collapse. To prevent this, caves larger than a certain size need to be filled with a special material before building the tunnel. This research helps make subway tunnel construction safer and more cost-effective in areas with karst caves.