Study on Mechanical Characteristics of Shield Tunnels in Composite Strata Considering Segment Parameters

［Objective］ The influence of longitudinal stratum differences on tunnel structure under complex strata conditions is often ignored in shield tunnel design, resulting in the problem that although the structural design may meet construction requirements in the short term, it is difficult to achieve service life in the long term. Therefore, it is necessary to study the tunnel mechanical properties considering the changes in segment structural parameters under longitudinal stratum differences. ［Method］ Based on a composite strata shield tunnel project of Nanning Metro Line 5, a three-dimensional longitudinal numerical model is established to calculate the mechanical response of the tunnel structure in composite strata, and to analyze the influence of segment width, longitudinal bolt strength and number of bolts on the mechanical characteristics of the tunnel. ［Result & Conclusion］ The influence range of strata mutation on the tunnel mechanical behavior is related to the overall longitudinal stiffness of the tunnel. Increasing segment width and the number of longitudinal bolts will expand the influence range of the tunnel mechanical behavior, but the bolt grade has little effect on this. A wide segment can effectively reduce the overall longitudinal stiffness of the structure, but increase the internal force response; compared with increasing the bolt grade, increasing the number of longitudinal bolts can more significantly improve the overall longitudinal stiffness of the tunnel structure and result in smaller structural deformation.