TBM stands for Tunnel Boring Machine. It is a specialized machine used for excavating tunnels in various types of ground conditions, including soil, rock, and mixed ground. TBMs are commonly used in civil engineering projects such as subway systems, underground transportation tunnels, sewage systems, and mining operations.

TBM technology has evolved over the years, and different types of TBMs are available to suit specific geological conditions. The basic principle involves the use of a rotating cutting wheel or disc with cutting tools or cutters that excavate the ground. The excavated material is then transported through the machine and removed from the tunnel.

TBMs offer several advantages over traditional tunneling methods, including increased speed and efficiency, reduced environmental impact, improved safety for workers, and the ability to create tunnels with smoother walls. They can operate in a continuous manner, excavating and lining the tunnel simultaneously, which reduces the need for extensive manual labor.

Overall, TBMs have revolutionized the field of tunneling and have become the preferred method for many large-scale tunneling projects around the world.