Abstract:  Current grouting-treatment projects for shield tunnels overly rely on a single indicator—horizontal convergence—precluding comprehensive and accurate evaluations of how the grouting treatment affects the asymmetric deformation of shield tunnels. To resolve this problem, the present authors incorporate asymmetric calculations into a method that evaluates the effectiveness of tunnel-grouting treatments. The method collects three-dimensional laser scanning point-cloud data of shield tunnels before and after grouting, denoises the point cloud, and applies segmentation methods. The full-section deformation of the tunnel is then calculated through multi-arc fitting, quickly acquiring indicators such as horizontal convergence, joint opening, and joint dislocation of the tunnel. Next, the authors propose an asymmetric deformation evaluation-index system based on the horizontal deformation difference I_H and the relative value i_H between the left and right sides of the tunnel segment and the center of the falling block. The calculated indices quantitatively characterize the asymmetry degree of tunnel cross-sectional deformation. In case-studies of the grouting treatment effect, the asymmetric deformation calculation using horizontal convergence as the sole evaluation criterion yields a 21% higher joint width of the tunnel segments after grouting than before grouting, leading to asymmetric deformation of the tunnel and threatening its structural safety.

Key words: shield tunnel, point-cloud solution, asymmetric deformation, grouting treatment evaluation