On June 20, accompanied by cheers from on-site construction workers, the Changfangzi Tunnel on the Chongqing-Kunming High-Speed Railway, built by China Railway Shanghai Engineering Group, was successfully holed through, marking the smooth breakthrough of the first low-gas tunnel over 4 kilometers long in the Yunnan-Guizhou section of the Chongqing-Kunming High-Speed Railway and laying a solid foundation for the early completion and opening of the Yunnan-Guizhou section of the line.

The Changfangzi Tunnel is located in Xundian County, Kunming City, Yunnan Province, with a total length of 4,285 meters, and is a low-gas tunnel. The tunnel has complex geological conditions, with unfavorable geology such as karst caves and faults, and it crosses over the Shimentong underground river while its exit passes beneath the Xunzhan Expressway, making construction extremely difficult. To ensure the safety of low-gas tunnel construction, the participating units formulated special construction plans, strictly implemented the safety technical specifications for gas tunnel construction, equipped an automated monitoring and information system for toxic and harmful gases, and strengthened gas monitoring and detection. At the same time, they intensified training and emergency drills for gas tunnel construction, improving safety awareness and emergency response capabilities through animated videos, safety technical briefings, and on-site drills. In response to the unfavorable geology, they adopted a "factory at the portal, workshop inside the tunnel" model, forming seven tunnel construction operation lines and achieving standardized operations across all tunnel construction processes, ensuring construction efficiency and quality.

The Chongqing-Kunming High-Speed Railway is an important component of the Beijing-Kunming corridor, one of the main corridors of China's "Eight Vertical and Eight Horizontal" high-speed railway network. The line starts from Chongqing West Station, passes through Chongqing Municipality, Sichuan Province, Guizhou Province, and Yunnan Province, and connects to Kunming South Station, with a total length of 699 kilometers, a design speed of 350 kilometers per hour, and a planned total of 21 stations. After the project is completed and opened to traffic, it will further improve the national comprehensive three-dimensional transportation network, strengthen the connection between the Chengdu-Chongqing economic circle and the central Yunnan region, significantly shorten the railway travel time from Chongqing to Kunming, greatly improve travel conditions for people along the line, and promote high-quality economic and social development along the route.