Abstract: To examine the influence of shield undercrossing on the circumferential deformation of an existing shield tunnel, the confining pressure redistribution model of the existing tunnel is improved. The improved model considers the stress relief, inter-ring shear force, and inter-ring tensile force of tunnel excavation to determine the circumferential load on the existing structure. Based on an engineering case, a refined three-ring segment model is established using Midas GTS NX finite element software to simulate the changes in the existing tunnel after confining pressure redistribution. The simulation results demonstrate the following: (1) The circumferential confining pressure of the existing tunnel decreases because of the proximity of the shield undercrossing. When the inter-ring shear and inter-ring tensile forces are considered, the additional circumferential confining pressure of the existing tunnel exhibits an asymmetrical distribution, forming an oblique figure-eight shape toward the crossing side. (2) Along the direction of the existing tunnel, the farther the distance from the crossing center, the smaller the absolute value of the additional confining pressure and the smaller the additional convergence value of the existing tunnel, which tends to zero at approximately Z₀ from the crossing center (where Z₀ is the buried depth of the existing tunnel). The existing tunnel changes the most at 210° and 330°, where the additional confining pressure decreases by 28.11 and 25.54 kPa, corresponding to change rates of 10.96% and 11.84%, respectively. (3) An increase in the soil loss rate correlates with a greater absolute value of the additional confining pressure and a larger additional convergence value of the existing tunnel. When the soil loss rate reaches 1.5%, the additional convergence value is 13.7 mm, and the change rate reaches 48.9%. (4) With increasing tunnel spacing, the absolute value of the additional confining pressure is smaller, and the additional convergence value of the existing tunnel is smaller. When the tunnel spacing is 7.6 m, the additional convergence value is 13.3 mm, and the change rate reaches 47.5%.

Key words: shield undercrossing, additional confining pressure, numerical simulation, additional convergence values, existing shield tunnel