Abstract: To explore the mechanical response of tunnel portal in mechanized construction of cross passage of shield tunnel, a threedimensional finite element numerical simulation is conducted on tunnel portal structure of cross passage, i.e.,  reinforced concrete segment reinforced by glass fiber + reinforced concrete composite segment, based on fullscale test, which considers the stress characteristics of segment during start, presupport, cutting, tunnel forming, and support dismantling process. Then the test data is compared with simulation results to validate its accuracy. The calculation results show the following: (1) The opening area at the main tunnel shows obvious stress concentration during cross passage breaking. (2) The cutting deforms after the opening is broken. (3) The maximum bending moment and axial force appear in the adjacent segments on both sides of the opening. (4) The concrete damage is mainly distributed in the inner camber of the arch crown and the outer camber of the arch waist at the opening side. Furthermore, a tunnel portal structure model of ring beam reinforcement is proposed, whose mechanical response during tunnel portal breaking of cross passage is compared with the abovementioned one. The comparison results show that the axial force and bending moment of the two structures vary little, but the lining displacement of the ring beam reinforcement structure is much smaller. The results demonstrate that the longitudinal structural stiffness of the tunnel can be improved by ring beam, and the differential deformation between segments can be effectively controlled during segment cutting process.

Key words: shield tunnel, mechanized construction of cross passage, segment lining, portal structure, numerical simulation