World-first U-shaped Tunnel Anchor Completed for Sichuan’s Lugu Lake Super Bridge
SICHUAN, 1 July — Construction has reached a core milestone on the Xichang-Shangri-La Expressway in Sichuan province, with the full breakthrough of a globally exclusive U-shaped rotary tunnel anchor at the Lugu Lake Super Bridge. As one of nine signature mega projects along the route, the pioneering structure delivers a critical breakthrough in the installation of the bridge’s main force-bearing system, laying a solid structural foundation for the world’s largest mountain suspension bridge.
Spanning the Woluo River in Changbai Town, Yanyuan County of Liangshan Prefecture, the Lugu Lake Super Bridge stretches 1,921 metres with a main span of 1,680 metres. It holds four world-leading engineering records, including the world’s longest-span mountain suspension bridge, the world’s longest-span spatial cable suspension bridge, the world’s longest-span suspension bridge equipped with tunnel anchors, and the tallest steel-concrete composite bridge tower among global mountain bridge projects.
The landmark engineering feats are matched by extreme construction difficulties. The tunnel anchor zone features entirely Grade V weak surrounding rock, densely distributed faults and fragmented rock mass. Multiple geological hazards including water seepage, karst cavities and mud surges coexist in the construction area, creating highly unstable ground conditions that pose severe challenges to conventional excavation and anchoring operations.
Traditional suspension bridge anchoring solutions rely either on massive concrete gravity anchors that restrain main cables by dead weight or linear tunnel anchors that grip cables via embedded rock bodies. These conventional designs proved unfeasible for the Lugu Lake Super Bridge, due to the narrow alpine canyon terrain and fragile local geology.
Engineering teams developed and applied the original U-shaped rotary tunnel anchor design, marking the first adoption of such technology worldwide. Removing the traditional rear anchor chamber structure, the innovative design connects the tail sections of two upstream and downstream anchor plugs to form a closed annular system. The integrated structure locks firmly into the mountain mass, cutting engineering volume by nearly 30 per cent while substantially improving overall force transmission efficiency and anchoring stability.
To adapt to the extremely fragmented rock strata, the construction team adopted an innovative reserved surrounding rock central grooving method. Advanced pre-support and steel frame reinforcement stabilise fragile rock formations before layered and phased excavation. Optimised mucking procedures and multi-process overlapping operations enable efficient construction within constrained site spaces. Digital analysis, three-dimensional technical disclosure and real-time dynamic monitoring systems are deployed throughout the works, delivering continuous geological data feedback. The integrated construction method successfully addresses technical bottlenecks in large-section rotary tunnelling under complex weak rock conditions, forming a replicable technical template for the construction of ultra-long-span mountain suspension bridges.
Operated and invested by Shudao Expressway Group and constructed by Sichuan Road and Bridge Group, the Xichang-Shangri-La Expressway represents the most technically challenging highway project currently under construction in Sichuan province. Stretching 233.13 kilometres, the dual four-lane expressway features a design speed of 80 kilometres per hour, with a total budget of approximately 58.7 billion yuan.
The route forms a key segment of the Greater Shangri-La tourist loop and serves as a vital transportation corridor linking inland southwest China with the Yangtze River Economic Belt, Chengdu-Chongqing Twin-city Economic Circle and Pearl River Delta Economic Zone. Upon full completion, the expressway will end the absence of high-speed road access in Yanyuan County and Muli Tibetan Autonomous County. It will further optimise the regional trunk highway network, upgrade transportation conditions for ethnic minority areas, support rural vitalisation development, and unlock local resource advantages to drive balanced regional economic and social progress.
