A tunnel boring machine (TBM) works by mechanically excavating tunnels through soil, rock, or sand using a rotating cutterhead at the front. This cutterhead, equipped with cutting tools or discs, rotates to break and remove earth or rock from the tunnel face. The excavated material (called spoil) is then transported away from the face by conveyor belts or screw conveyors inside the machine.
Behind the cutterhead is a shield that supports the tunnel walls as the machine advances. The TBM uses hydraulic jacks to push itself forward into the newly excavated space, pressing against the concrete segments that it installs to line and support the tunnel walls. These precast concrete segments are placed and connected to form a sturdy tunnel lining, with gaps filled by grout to keep out water.
The TBM operates continuously in a cyclic process: excavate with the cutterhead, remove spoil, advance forward with hydraulic thrust, and line the tunnel walls with concrete segments. This mechanized process allows for faster, safer, and less disruptive tunnelling compared to traditional drilling and blasting methods. The typical tunnel shape is circular, but TBMs can also create other shapes depending on design.
Tunnel boring machines are equipped with advanced navigation systems and operate deep underground with minimal surface disruption, making them ideal for urban tunnelling projects. Modern TBMs can tunnel up to 10 meters per day, with some soil and rock models reaching hundreds of meters per week depending on conditions.
