Abstract: To achieve millimeter-level real-time positioning of an "integral underwater thrust-type" closure joint in the Shenzhen-Zhongshan link immersed tunnel, which operates under complex subaqueous environments, the authors propose a hybrid positioning method that combines binocular camera vision with angle and distance measurements using a laser-wire system. The binocular camera system, in conjunction with the laser-wire system, facilitates the real-time acquisition of attitude and position data for the closure joint during the thrusting process. Integrating the results from in-tube surveys, high-precision underwater real-time positioning of the closure joint is achieved. The binocular camera vision system captures three-dimensional (3D) displacements of feature points, and the laser-wire system measures angles using a laser and distances using an encoder. These measurements allow for the real-time calculation of 3D coordinates for the feature points. In addition, a positioning and monitoring system is developed for the immersed tunnel, which includes hardware, software, and protocols. The hardware integrates the binocular camera-laser wire composite units with synchronous controllers, and the software creates a 3D visualization interface and data management platform. This system enables real-time monitoring and redundant measurement of the 3D attitude in a semi-enclosed space. Verification through onshore push-back tests, underwater heavy-load tests, and field installations demonstrates that the positioning accuracy of the system is within 10 mm, meeting the installation accuracy requirements for the closure joint. This approach addresses the challenges faced by traditional global navigation satellite system real-time kinematic (GNSS-RTK) survey tower positioning systems, which are difficult to apply in narrow, semi-enclosed, and restricted underwater spaces. It also overcomes the limitations of traditional GNSS-RTK and sonar technologies in these environments, providing a viable high-precision dynamic positioning solution for the installation of large-tonnage components underwater.

Key words: Shenzhen-Zhongshan link, immersed tunnel, closure joint, binocular camera, underwater laser-wire system