On the morning of September 14, an important progress was made in the Chongqing-Kunming High-Speed Railway, a key component of China's "Eight Vertical and Eight Horizontal" high-speed rail network. After more than 1,000 days of arduous construction by the builders, the Tongchangqing Tunnel of the Chongqing-Kunming High-Speed Railway, constructed by China Railway 12th Bureau Group, was safely holed through. So far, 25 of the 63 tunnels in the Yunnan section of the Chongqing-Kunming High-Speed Railway have been holed through, laying a solid foundation for the completion and opening of the entire Chongqing-Kunming High-Speed Railway.

The Tongchangqing Tunnel is located at the junction of Huize County and Xundian County in Yunnan Province, with a total length of 5.2 kilometers and a maximum buried depth of 280 meters. It is a single-tube double-track tunnel. The tunnel is situated in the northeastern Yunnan mid-mountain area of the Yunnan-Guizhou Plateau, where mountains overlap and gullies crisscross, with complex and changeable terrain. In addition, the tunnel passes through a variety of complex geological conditions, making it a typical karst tunnel. During construction, mud bursts, water inrushes and karst caves occurred frequently, with a total of 13 incidents of mud bursts, water inrushes and karst caves, posing unprecedented challenges to construction.

In response to construction difficulties such as large variations in the surrounding rock of the karst tunnel and the strong suddenness of mud bursts and water inrushes, science and technology were taken as the guide and innovation as the driver. The detection range of advanced geological forecasting was innovatively expanded, and the accuracy of geological identification was enhanced. At the same time, measures such as rapid advanced support, strict control of excavation footage and strengthened initial support were implemented, ensuring the safety and quality of tunnel construction. The excavation of Class IV and Class V surrounding rock at the tunnel entrance advanced steadily at an average rate of 80 meters per month, ultimately achieving the safe holing-through of the tunnel.

During the construction of the Tongchangqing Tunnel, the construction unit adopted a construction method combining micro-seismic blasting excavation with surface deformation monitoring, which effectively reduced the disturbance of construction to the surrounding unstable rock mass. This not only ensured construction safety but also accumulated valuable experience for the construction of similar tunnels. At the same time, tunnel construction also faced tests from natural conditions such as remote geographical location, inconvenient transportation and rising water levels during the flood season. Since the start of the project, the construction team has responded actively and taken the initiative, building a temporary construction bridge at the tunnel portal and constructing winding mountain access roads, effectively solving the problem of material transportation and ensuring the smooth progress of construction.

The Chongqing-Kunming High-Speed Railway is a key component of the Beijing-Kunming corridor of the national "Eight Vertical and Eight Horizontal" railway network, with a total length of 699 kilometers, of which the Yunnan section is 388.6 kilometers long. As the first high-speed railway in Yunnan Province designed with a speed of 350 kilometers per hour, after the entire line is completed and opened to traffic, the travel time from Chongqing to Kunming is expected to be shortened from the original 5 hours to about 2 hours at the fastest.