Study On Displacement Monitoring System For Tunnel Vault Based On Digital Image Processing

With the development of national economy, the tunnel project is also developing rapidly. For the tunnel project, the Construction supervision and measurement is an essential part of project construction. Among them, the crown settlement measurement is an important way of confirming the stability of surrouding rock and forecasting the crown collapse. Therefore, accurately and timely obtaining the crown displacement is particularly important. For the crown settlement measurement, there are a lot of methods which are playing an important role in project construction, but these methods do not achieve the unity of accuracy, operation and cost. Thereofore, with the requirement of crown displacement monitoring, we design a system which is constituted by digital camera and electronic theodolite, derive the realization principle of this system, and develop the monitoring software which is compatible with this system. Through this system, we hope to achieve the unity of accuracy, operation and cost.In this system, we make the electronic theodolite which is combining with a digital camera as measuring tool, and design the calibration board compatible with this system. In the system application, we place the target calibration board in the position which should be monitored (for the tunnel project, people usually choice tunnel crown as the position), and place the reference calibration board in the datum point. This system achieving is consisted by the following steps: First, use the digital camera to obtain the pictures of target calibration board and reference calibration board, combining with the digital image processing, realize camera calibration and obtain the coordinate of optical center. Second, use the coordinate of optical center and the angle obtained by electronic theodolite to calculate the coordinate of theodolite center (three aixs intersection). Third, use the coordinate of theodolite center and the angle between the two calibration boards to calculate the three-dimensional coordinate between the target calibration board center and the reference calibration board center. Finally, through the long-term monitoring to these calibration boards, we can obtain the there-dimensional displacement of target calibration board center, and draw their displacement-time diagrams.Verified by multi-groups expriements, we can kown that the principle of this system is right and this system has the characteristics of free stationing. This system basically achieves the unity of accuracy, operation and cost, and provides a more ideal method of crown displacement monitoring for tunnel project construction.