Analytical solution to the mechanical response of grouting lifting in existing shield tunnels and engineering case verification

Grouting lifting is the effective approach for treating differential settlement of existing tunnels, but it easily deteriorates the tunnel structure again and seriously threatens the operational safety of urban rail transit. Aiming to solve the above problem, this paper considers the interaction between the tunnel and the foundation, and establishes a series of analytical solutions of the stress, strain, axial force, and bending moment of the tunnel under single point grouting. Based on the characteristics of shield tunnel correction engineering and the analytical solution under single point grouting, the equation of the internal force and deformation of tunnel structure under multi-point grouting considering different grouting angles and different strata is obtained. The grouting correction engineering case for Shenzhen Metro Line 1 shows that the analytical solution to the displacement of the tunnel structure is well matched with the measured displacement of the tunnel structure is well matched with the measured data of the case and the difference is less than 15 %. The parameter analysis results indicate that the main loaded area of the tunnel under single point grouting is related to the stratum, and the main loaded area of the soft soil stratum is -42.4°+42.4° around the grouting point. Convergence deformation of the tunnel under multi-point grouting reaches the maximum value at the diameter passing through the center of the grouting zone and the minimum value at the diameter which is perpendicular to the former. Under the condition of limiting horizontal convergence deformation, the reasonable grouting angle range of the multi-point grouting zone is about 120°150°. This paper provides a theoretical basis that can immediately evaluate the mechanical structure performance and to determine whether to impose greater pressure when the tunnel is continuously lifted.