The shield section of the Chongqing Caiyuanba Yangtze River Tunnel of the Chongqing-Xiamen High Speed Railway has been successfully completed. Located on the Chongqing-Chongqingdong segment of the line, it is the first high-speed railway tunnel under the Yangtze River in the upper reaches. The tunnel has a total length of 11.9 kilometers, running beneath municipal roads, viaducts, metro lines, multiple building clusters and the main navigation channel of the Yangtze River, with the river-crossing section stretching 1,282 meters. The project overcame major technical challenges such as the precise in-tunnel assembly and launch of a 3,500-ton large-diameter shield machine, filling a critical gap in industry technology.