After 1,200 days and nights of intensive work, at 7:38 a.m. on December 5, with the sound of an explosive blast, 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, was successfully holed through, 4 months ahead of the planned schedule. This marks that the remaining works of the main tunnel (the main structure of the tunnel, i.e., the tunnel through which trains run) have entered the sprint stage, laying a solid foundation for the breakthrough of the entire 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 Guinan High-Speed Railway and even in Southwest China, and is also one of the most difficult high-speed railway tunnels to build in Southwest China. It is the No. 1 controlling project of the entire line and a Level I risk management tunnel. Construction started on September 9, 2018.

"The Jiuwandashan No. 1 Tunnel passes through an area with complex and variable geological structures. Soluble rock sections account for 85.9% of the entire tunnel, with karst development ranging from moderate to strong. It crosses over a regional underground river, and a large number of depressions have developed on the surface, resulting in an extremely high risk of water and mud inrush." According to the person in charge of the Guinan High-Speed Railway Project Department of China Railway 18th Bureau, 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 holed through this time has a total length of 9,228 meters and is one of the key projects of the entire Guinan 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. Construction was highly difficult, safety risks were high, and schedule pressure was heavy.

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, overcoming a series of difficulties such as complex geological conditions and inconvenient transportation, and setting off an upsurge of labor competition. It achieved an average monthly advance of 240 meters and set the highest record on the entire line with a maximum monthly advance of 330 meters, holing through 4 months ahead of the planned schedule.

"The breakthrough of the parallel adit will increase the working faces for main tunnel construction, greatly improve the construction organization, material transportation, and tunnel ventilation conditions of the main tunnel, and effectively avoid risks such as water inflow, sand inflow, and mud inrush in the main tunnel." According to the person in charge of the project department, 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 of the main tunnel will be rapidly advanced, and the breakthrough of the entire tunnel is just around the corner.

The Guinan High-Speed Railway is the first high-speed railway in Guizhou Province designed with a speed of 350 kilometers per hour. It is a component section of the Baotou-Haikou corridor, one of the main "eight vertical and eight horizontal" 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 Guinan High-Speed Railway opens to traffic, the fastest high-speed train journey from Guiyang to Nanning will be shortened 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 line.