Abstract: Large-diameter single-tube double-track shield tunnels with middle partition walls face significant challenges such as difficult left- and right-line laser scanning point cloud data registration and low convergent deformation measurement accuracy. To address these challenges, a point-cloud data positioning algorithm that automatically identifies the circumferential joints of the shield tunnel segments is constructed. In addition, a full-local dynamic iterative point-cloud automatic registration method for shield tunnel segment rings is proposed. This method minimizes the deviation of tunnel structure feature points and distances, thus achieving precise fusion of the full-loop point cloud data of the corresponding left and right line segments of the tunnel. The overall horizontal convergent deformation of the shield tunnel with middle partition walls is determined by applying noise reduction and distance least squares elliptic fitting to the fused full-loop point cloud data of the segments. Integrating a point cloud data fusion algorithm facilitates the development of a rail transit tunnel structure inspection vehicle TDD-SD equipped with a three-dimensional laser scanner and supporting data processing software. Finally, engineering pilot applications and manual comparison verification are performed. The results demonstrate that at a measurement speed of 20 km/h, the maximum absolute deviation between the mobile measurement of the tunnel horizontal convergent deformation detection vehicle and the manual measurement is 2.0 mm. This represents a ratio of 0.16‰ to the outer diameter of the tunnel, demonstrating good consistency between the two measuring methods. The mobile measurement accuracy meets the industry standards for evaluating the impact of segment convergent deformation in large-diameter shield tunnels. The feasibility of the proposed point-cloud data fusion algorithm for the left and right line segments is also validated.

Key words: single-tube double-track shield tunnel, large-diameter shield tunnel, middle partition wall, mobile measurement, convergent deformation, data registration and fusion