Tunnel boring machines (TBMs) are guided using a combination of advanced surveying, navigation, and control systems. These methods ensure that the machine follows the planned tunnel route accurately, even in challenging underground conditions. Here's how it works:

　　1. Laser Guidance Systems

　　- Laser-based navigation: A laser beam is fixed at the tunnel’s starting point and projected along the tunnel's planned alignment. The TBM is equipped with a laser target or sensors that continuously monitor the laser’s position.

　　- Deviation detection: If the TBM veers off course, the sensors detect the deviation, allowing operators to correct the machine's heading by adjusting the steering mechanisms.

　　2. Gyroscopic Navigation

　　- Inertial navigation systems (INS): These use gyroscopes and accelerometers to measure the TBM’s position and orientation in real time. Since these systems don't rely on external signals, they can work in deep tunnels where GPS is unavailable.

　　- Continuous position updates: The INS provides ongoing data about the TBM’s movement, helping maintain an accurate position even over long distances.

　　3. Control Systems and Steering

　　- Hydraulic rams and articulation: TBMs are equipped with hydraulic rams that can steer the machine by pushing against the tunnel walls or adjusting the position of the cutter head.

　　- Automated steering: Many modern TBMs use computerized control systems that automatically make small adjustments based on real-time data from the navigation systems.

　　4. Real-Time Monitoring

　　Sensors installed on the TBM collect data about the machine’s position, orientation, and performance. This data is fed into computer systems where it is analyzed in real-time to make adjustments to the steering and cutting process.

　　5. Surveying and Mapping

　　- Regular surveys: Surveyors periodically check the TBM’s progress using traditional survey techniques, like theodolites, to ensure that it remains on the planned route.

　　- 3D mapping technology: Some TBMs use sophisticated 3D mapping tools (like LIDAR or ground-penetrating radar) to create real-time models of the tunnel, which can be compared to the design and adjusted if needed.

　　6. Ground Monitoring

　　- Geological sensors: TBMs are often equipped with sensors that monitor the surrounding ground conditions, such as pressure, density, and moisture. These readings are vital for ensuring the TBM moves through different soil or rock types safely and without deviation.

　　7. Communications System

　　Communication between the TBM operators inside the machine and the surface team is crucial. Advanced communication systems keep everyone informed about conditions underground, allowing for timely decision-making.

　　8. Feedback Loop

　　All collected data forms part of a continuous feedback loop. Engineers analyze this data not only to guide the current project but also to refine techniques for future tunneling operations.

　　These systems work together to keep the TBM on its precise path while tunneling underground.