# The Development of the Pipe Jacking Guidance Technology
## 4 Prism Method
### Research Status  
At present, the MTG-P3 pipe jacking guidance system of Shanghai MIDU Measurement Technology Co., Ltd. (Shanghai, China) realizes the measurement of the position and posture information of the pipe jacking machine through a high-precision total station and three prisms. The high-precision laser total station and prisms are installed on the wall of the starting shaft and on the top of the pipeline with a bracket. Three prisms are installed at the tail of the pipe jacking machine and placed in a triangle, namely the target prisms. The prisms with known coordinates are placed on the wall of the starting shaft and are used for aiming at the orientation in front of the target prisms, namely the rear-view prism. During operation, the control terminal is used to control the total station to aim at the rear-view prism. After completing the rear-view orientation, the target prisms should be aimed at sequentially to obtain the coordinate information of the three target prisms in the absolute coordinate system. Therefore, the coordinates of the center of the tail of the pipe jacking machine are deduced, and the coordinates of the center of the head of the pipe jacking machine are deduced by using the structural relationship of the pipe jacking machine. Consequently, the attitude information of the position of the pipe jacking machine can be obtained. During the construction process, as the pipe jacking machine moves forward, the total station and the target prisms move together. The total station measures the positional coordinates of the prisms in real time and transmits the measurement data back to the control terminal. This results in the real-time position information of the pipe jacking machine. The ROBOTEC automatic guidance system of Japan's ENZAN company (Kyoto, Japan) has the same principle. Through professional software data processing, the plane deviation, elevation deviation, slope and other information between the center axis of the pipe jacking machine and the design axis of the pipeline are displayed in real time on the screen.  
For dynamic measurement during pipe jacking construction, the total station cannot aim at three prisms at the same time, and each prism needs to be searched and measured in turn. As the pipe jacking machine keeps moving forward, it causes the measurement position of each prism to be out of synchronization. Secondly, the confined space within the jacking pipe, coupled with inadequate spacing between prisms, led to suboptimal calculation accuracy and constrained viewing conditions.  
In response to the above problems, relevant research has been carried out to design prediction algorithms to reduce the errors caused by unsynchronized measurement times for the problem of unsynchronized prism measurements. In response to the problem of not being able to install three target prisms, the \"Two prisms--Inclinometer\" scheme was  
Figure 10: Schematic diagram of the rolling Angle calculation.  
adopted, which reduces the number of prisms and adds a smaller inclinometer with fewer placement restrictions to complete the guided measurement.