Investigation into the Influence of Overlapping Shield Tunnel Crossing on the Circumferential Internal Forces of an Existing Tunnel

To study the changes in circumferential internal forces of an existing shield tunnel when an overlapping tunnel passes through, a surrounding pressure redistribution model for overlapping tunnels was established to calculate the circumferential surrounding pressure of the existing tunnel. Combined with an engineering case, a detailed three-segment tunnel model was created using Abaqus 2023 finite element software. The circumferential forces of the tunnel were applied to the model, and the circumferential internal forces of the segments were extracted to study the variation law of segment circumferential internal forces. The research results indicate the following: (1) During the excavation of overlapping tunnels, the circumferential surrounding pressure of the existing tunnel decreases, and the circumferential surrounding pressure at any position exhibits a symmetric “8”-shaped distribution. (2) During the excavation of the new tunnel, the circumferential internal forces of the existing shield tunnel increase. In front of the excavation face, the additional internal forces of the tunnel decrease with distance, while within approximately 6 m behind the excavation face, the additional internal forces of the tunnel increase sharply. (3) As the angle between the line connecting the axes of the two tunnels and the z-axis increases, the additional internal forces of the existing tunnel decrease; as the clear distance between tunnels increases, the circumferential internal forces of the existing tunnel decrease, and the additional bending moments and additional shear forces approximately show linear variation.