Support Characteristic of a Novel Type of Support in Loess Tunnels Using the Convergence-Confinement Method

摘要

The convergence-confinement method (CCM), a widely used tunnel design method, is an analysis approach that can intuitively reflect the interaction between the surroundings and the support in tunnels. In this article, the CCM approach is used to determine the support performance of a steel-concrete composite support (SCCS) system, which is characterized by an improved stiffness of the initial support due to its unique arch type (pi-type) and construction steps. In view of the tunneling process, the support characteristics of a conventional support system and the SCCS system are determined from the perspectives of single and combined support structures. A sensitivity analysis by considering the arch installation spacing, wall thickness, and concrete grade is performed. The results reveal that the stiffness and support pressure of the hollow pi-type steel arch increase linearly with a decrease of the installation spacing and an increase of the wall thickness, while its support performance only slightly improves with an increase of the inner concrete grade after filling with concrete. Additionally, the support characteristic curves for different support systems are obtained, and the safety factor of the SCCS system is found to be greater than 3.48. The maximum support pressure of the SCCS system is found to increase by 1.25 MPa and its support performance increases by 4.57 times as compared to those of the conventional support system. Finally, the construction technology of the SCCS system is discussed, and some application suggestions are provided. (c) 2021 American Society of Civil Engineers.