After 1,200 days and nights of intensive work, at 7:38 a.m. on December 5, a blast marked the successful breakthrough of the parallel adit at the exit of the Jiuwandashan No. 1 Tunnel on the Guiyang-Nanning High-Speed Railway, constructed by China Railway 18th Bureau Group. The breakthrough came four months ahead of the planned schedule, marking the entry of the remaining works on the main tunnel (the main structure of the tunnel, i.e., the tunnel through which trains run) into the sprint stage and laying a solid foundation for the full breakthrough of the tunnel.

The Jiuwandashan No. 1 Tunnel is located in Libo County, Qiannan Autonomous Prefecture, Guizhou Province. With a total length of 17,012 meters (17.012 kilometers), it is the longest tunnel on the entire Guiyang-Nanning High-Speed Railway and in Southwest China, as well as one of the most difficult high-speed railway tunnels to build in Southwest China. It is the No. 1 controlling project and a Level I risk management tunnel of the entire line, and construction began on September 9, 2018.

The Jiuwandashan No. 1 Tunnel passes through an area with a complex and variable geological structure. Soluble rock sections account for 85.9% of the entire tunnel, with karst development ranging from moderate to strong. The tunnel crosses over a regional underground river, and numerous depressions have developed on the surface, resulting in an extremely high risk of water and mud inrush. To ensure construction safety and progress, the project department adopted an auxiliary tunnel mode of "2 cross adits + 1 drainage adit + 2 ventilation shafts + 1 exit parallel adit" for tunnel construction.

The parallel adit is an auxiliary tunnel (working face) added for the construction of the main tunnel (main adit). The parallel adit that broke through this time has a total length of 9,228 meters and is one of the key projects of the entire Guiyang-Nanning High-Speed Railway. It runs parallel or approximately parallel to the main tunnel and connects with the drainage adit at DK184+800. It was excavated from two work areas in opposite directions. From the start of construction on July 15, 2018, to the day of breakthrough, the parallel adit passed through 6 sets of strata, 2 faults, and 1 contact zone, and encountered 260 karst caves of various sizes. The construction was highly difficult, with high safety risks and heavy schedule pressure.

In response to the difficulties, the project department, through standardized management, refined control, and scientific organization, applied multiple measures such as a process assessment system, information-based management methods, smooth blasting control, and research on rapid excavation. It overcame a series of difficulties, including complex geological conditions and inconvenient transportation, and set off an upsurge of labor competitions. The project achieved an average monthly advance of 240 meters and set the line's highest record of 330 meters in a single month, breaking through four months ahead of the planned schedule.

The breakthrough of the parallel adit will increase the working faces for the main tunnel, greatly improve the construction organization, material transportation, and tunnel ventilation conditions of the main tunnel, and effectively avoid risks such as water, sand, and mud inrush in the main tunnel. As of December 4, the cumulative excavation of the main tunnel of the Jiuwandashan No. 1 Tunnel had reached 14,225.9 meters, accounting for 84% of the total length, with only 2,786.1 meters remaining. After the breakthrough of the parallel adit, the remaining works on the main tunnel will be advanced rapidly, and the full breakthrough of the tunnel is just around the corner.

The Guiyang-Nanning High-Speed Railway is the first high-speed railway in Guizhou Province designed for a speed of 350 kilometers per hour. It is a component section of the Baotou-Haikou corridor, one of the "eight vertical and eight horizontal" main high-speed railway corridors in the National Medium- and Long-Term Railway Network Plan. The main line has a total length of 482 kilometers, including 199 kilometers in Guizhou and 283 kilometers in Guangxi. The entire line is expected to meet the conditions for opening to traffic by the end of 2023.

After the Guiyang-Nanning High-Speed Railway opens to traffic, the fastest high-speed train journey from Guiyang to Nanning will be reduced from the current more than 5 hours to less than 2 hours. It will play an important role in improving Guizhou's high-speed railway network, improving travel conditions for people along the line, and promoting rural revitalization and high-quality economic and social development in various places along the route.