On the morning of June 18, after more than 1,000 days of arduous construction, the exit and the cross-adit section of the Nazhaqing Tunnel on the Chongqing-Kunming High-Speed Railway were connected ahead of schedule. The smooth breakthrough of this key section not only greatly improves construction efficiency but also lays a solid foundation for the full breakthrough of the tunnel, marking the start of the final 300-meter sprint.

The Nazhaqing Tunnel is located in Huize County, Yunnan Province, with a total length of 7,268 meters. It is the only extra-long shallow-buried tunnel exceeding 7 kilometers in Yunnan Province. The tunnel passes through complex geological structures, including water-rich basalt intercalated with tuff strata and three fault zones. The tunnel body traverses six shallow-buried sections and passes beneath surface water flows and buildings at five locations, with a minimum burial depth of only 14 meters. Construction faces extremely high risks of water seepage and mud and water inrush, making the project exceptionally difficult to build.

Liu Miao, on-site manager of the Chongqing-Kunming High-Speed Railway project for China Railway 12th Bureau Group, said that the construction method combining "micro-seismic blasting excavation and surface deformation monitoring" was adopted on site, successfully passing through the shallow-buried sections and the sections beneath surface buildings, accumulating experience for the construction of tunnels with similar geological conditions.

As the first high-speed railway in Yunnan Province designed for a speed of 350 kilometers per hour, the Chongqing-Kunming High-Speed Railway will connect Yunnan, Guizhou, Sichuan, Chongqing and other provinces and municipalities. Once the entire line opens to traffic, the travel time from Chongqing to Kunming is expected to be shortened from the original 5 hours to about 2 hours, which will greatly promote the high-quality development of the regional economy.