The main tailrace tunnel of the Xiangjiaba right bank underground power station has the biggest designed cross-section dimension of its kind in the world. Due to this fact, its construction is complex. The principle of "top arch" lining first, then "excavation down" was adopted based on the location conditions during construction and thus addressed the issue of super-big cross-section tunneling works. The safety monitoring data of the project indicate that the stress strain develops in line with the project development law and demonstrate that the parameters designed for the excavation and support are reasonable. Construction safety meets the design requirements and the tunnel remains safe and stable. Therefore, the method for this tailrace tunnel can be used as a reference for other similar projects.
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