Mechanical response of large-diameter shield tunnels during assembly

Based on loading analysis of shield tunnel segments during the assembly phase, a finite difference model is established for segmental lining structure in assembly stage. The mechanical response of segments during assembling is analyzed regarding the in-situ test results of Shiziyang Intercity Railway Tunnel Project from Foshan to Dongguan. The results show that: (1) The measured values of axial force of segment monitoring section are mainly under compression during assembling process, but in the initial stage of assembling, the local tension exists and the calculated values are under compression. The measured and calculated values of bending moment show obvious positive bending trends. (2) The maximum measured values of axial force, positive bending moment and negative bending moment of segments after the ring is formed are about 1.5 times, 1.28 times and 1.36 times the calculated values, respectively. (3) The response of segment bending moment is more sensitive to assembly process than that of axial force. (4) The adjacent block assembly has the most significant effects on the axial force and bending moment of the segment, and the effects of F block insertion are subordinate. Other assembly steps have less influences, and the closer to the adjacent block and F block, the greater the internal force response. (5) The calculated and measured values of segment axial force and bending moment are approximately symmetrical along the radial central axis of the capping block after assembly, and the symmetry of the calculated values is more obvious than the measured values in the assembly process. (6) During the assembling process, the maximum measured axial force reaches 43.5% of the maximum calculated value of the beam-spring model in the serviceability limit stage, however, the maximum positive and negative bending moments reach 188.89% and 447.84%. It is indicated that the internal force response during assembling process is at a higher level during construction, which makes the segment often in a disadvantageous condition of large bending moment and small axial force when tunneling in full-face rocks. It is rational to pay more attention in design and construction.