At 9:30 a.m. on April 8, with the final blast, the Xiaoxinjie Tunnel of the Yunnan-Guizhou section pre-station Bid 8 project of the Chongqing-Kunming High-Speed Railway, constructed by China Railway 16th Bureau, was successfully holed through. Thirty minutes later, the Chenjia Tunnel also achieved safe holing-through.

　　The Chongqing-Kunming High-Speed Railway has a total length of 699 km, of which the Yunnan section is 388.6 km long and is the first high-speed railway in Yunnan Province designed for a speed of 350 km/h. The Yunnan-Guizhou section pre-station Bid 8 project undertaken by China Railway 16th Bureau Group is located in Xundian County and Songming County of Kunming City, with a line length of 30.354 km. Its main works include 3 tunnels, 25 bridges, 27 subgrade sections, and 801.64 km of single-track track laying. Up to now, all three tunnels within the project department's jurisdiction have been holed through, and the construction of bridge pier and abutment bodies has also been basically completed; girder erection is now under way, and the main line is expected to be holed through in April 2025.

Xiaoxinjie Tunnel

Chenjia Tunnel

　　The Xiaoxinjie Tunnel and Chenjia Tunnel in the Yunnan-Guizhou section of the Chongqing-Kunming High-Speed Railway are both double-track single-tube tunnels in Class V surrounding rock, where the rock mass is broken and prone to deformation. Among them, the Xiaoxinjie Tunnel has a total length of 2,045 m, with the rock strata dominated by strongly weathered mudstone and intercalated sandstone; the Chenjia Tunnel has a total length of 2,026 m, with the rock strata dominated by strongly weathered sandstone and shale. Construction risks are high and difficulty is great, and risks such as collapse and surrounding-rock deformation are highly likely, making these key controlling works of the project. To overcome the adverse effects brought by the geological conditions, the project team carried out tunnel excavation in strict accordance with the principles of "advance pipe forepoling, strict grouting, short advance per round, weak disturbance, strong support, rapid closure, frequent measurement, and timely lining follow-up," and adjusted the construction procedures in real time according to advanced geological forecasting, on-site surrounding-rock conditions, and safety step-distance management, thereby shortening the time for procedure connection, achieving refined management, scientific construction, and an orderly site, and holing the tunnels through one month ahead of schedule.

　　After the entire Chongqing-Kunming High-Speed Railway is completed and opened to traffic, it will run through Yunnan, Guizhou, Sichuan, Chongqing and other provinces and municipalities, becoming a convenient major corridor for Southwest China's opening-up and the joint building of the "Belt and Road," and is of great significance for promoting high-quality regional economic development, driving resource development and industrial development, and boosting rural revitalization and ethnic unity and progress.