# The Development of the Pipe Jacking Guidance Technology
## 6 Hybrid Method  
Since the laser propagates in a straight line and the dispersion of the laser spot formed by the laser affects the accuracy as the distance increases, the total station is too far away from the prism and cannot aim at the prism. In long-distance, curved pipe jacking construction, a single method is difficult to meet the guidance requirements. Therefore, the company that developed the pipe jacking guidance system proposed a hybrid guidance system with different schemes, which improved the guidance accuracy by combining multiple methods. Since a single prism mounted on the tail of the pipe jacking machine can only obtain the center coordinates of the tail of the pipe jacking machine, it cannot obtain the 3D orientation of the pipe jacking machine, which can be provided by an inertial device for orientation. [PERSON] [27] proposed a single prism and inertial measurement unit scheme. A prism is set up at a fixed distance above the center of the tail of the pipe jacking machine, a total station is placed inside the pipeline for coordinate measurement and a prism is set up on the top of the total station for elevation measurement with the prism at the tail of the pipe jacking machine. Since a single prism mounted on the tail of the pipe jacking machine can only obtain the center coordinates of the tail of the pipe jacking machine, it cannot obtain the 3D orientation of the pipe jacking machine, which can be provided by an inertial device for orientation. This solution realizes long-distance and curved pipe jacking guidance. The prism method and the laser target method are used in the TUnIS Navigation MTLaserTotalstation of VMT and the MTG-L pipe jacking guidance system of Shanghai MIDU Measuring Technology Co. The guidance system is divided into two working modes: short-distance, straight-line operating mode and long distance, curved-line operating mode (as shown in Figures 14 and 15). During pipe jacking construction, the total station installed in the starting shaft aims at the laser target that moves with the pipe jacking machine. The system is based on the laser target guidance principle and incorporates an odometer to provide distance information for the laser target method. As the distance increases or when encountering a bend, the laser is unable to be aimed at the laser target. At this time, the total station is set up in the pipeline and moves with the pipe segment. Two prisms are added, and a rear-view prism is set up in the starting shaft. The prism method and the laser target method are combined to guide the pipe jacking. Since the total station is used in long-distance pipe jacking, the total station must be placed inside the pipe according to the jacking distance and advanced with the pipe. For narrow pipes, the total station cannot enter the inside of the pipe. Therefore, VMT's TUnIS Navigation MTGyro uses a combination of laser target, odometer, static leveling and gyroscope measurements (as shown in Figure 16). The odometer and static leveling provide distance and elevation information. In the initial phase, the laser target method is employed to facilitate pipe jacking guidance. When the laser emitt  
Figure 14: Short-distance, straight-line operating mode. shaft is unable to reach the target, the inertial guidance method is utilized in replacement. Ultimately, curved and long-distance pipe jacking guidance is achieved. In addition, the TUnIS Navigation MTGyroEMS system developed by VMT based on gyroscopes and magnetic sensors is suitable for small-diameter, inaccessible long-distance and curved pipelines with high position accuracy. For construction conditions where visibility is not possible, the system uses an optical gyroscope as the main system and a magnetic sensor based on an electromagnetic probe as an auxiliary measurement system to perform comprehensive measurements.