Mechanism effect of umbrella arch supports in a shallow long-span tunnel: a case study.

When a tunnel passes through weak and fragmented surrounding rock, excavation disturbance can lead to significant deformation. To mitigate this, advanced support measures like the umbrella arch are necessary. This study investigates the effectiveness of the umbrella arch in controlling deformation of the surrounding rock, focusing on the super shallow-buried spillway section of the Shenzhen East Transit Expressway in China. Both numerical modeling and field monitoring were used to assess the support effect of the umbrella arch. The mechanism of the support was analyzed, revealing that the umbrella arch primarily prevents collapse of the surrounding rock by creating a small compression area. It is recommended that a starting segment with the same length as the tunnel diameter be reserved for the construction of long umbrella arches to maximize their supporting effect. The proposed numerical model was calibrated using field monitoring data, and the mechanical responses of an 80-m-long umbrella arch during construction were thoroughly analyzed. The research results presented in this paper can serve as a reference for the design of umbrella arches in similar projects in the future. [ABSTRACT FROM AUTHOR]