This is the excavator used to tunnel into the mines and to dig out new homes.
The excavator is driven forward by the caterpillar tracks while the excavator belt on the front section rotates and the teeth on the belt digs out the earth in front. It is the circular wheel at the top that leaves the characteristic semicircular shape on the roof of the dugout. And the circular markings on the walls are made by the wheels carrying the caterpillar tracks.
