On August 31, the section from No. 1 cross adit to the tunnel entrance of the Nanzhushan Tunnel in Section 6 of the pre-station works of the Chongqing-Qianjiang section of the Chongqing-Hunan High-Speed Railway was safely holed through, marking another breakthrough in the construction of the Nanzhushan Tunnel, a major and difficult project on the entire line.

The main line of the Chongqing-Qianjiang section of the Chongqing-Hunan High-Speed Railway is 269.5 km long, with a design speed of 350 km/h. The line in Section 6 of the pre-station works of the Chongqing-Qianjiang section of the Chongqing-Hunan High-Speed Railway is 28.478 km long, and its main construction content includes 10 tunnels, 10 bridges and 1 station. The proportion of bridges and tunnels is as high as 92.5%. The line passes through multiple geological fault zones, karst cave groups and gas-bearing zones, with complex geological conditions and extremely great construction difficulty.

The Nanzhushan Tunnel is located in Nanchuan District, Chongqing, with a total length of 10,794 meters, and is the longest tunnel in this section. The section from No. 1 cross adit of the Nanzhushan Tunnel to the entrance of the Nanzhushan Tunnel holed through this time is a 1,480-meter-long gas tunnel, all in Class IV and Class V surrounding rock, with poor geological conditions.

The construction contractor adopted the benching method for construction operations and strictly carried out gas work area management, implementing 24-hour automatic gas monitoring. At the same time, it actively applied the "three major emergency systems for railway tunnel construction" to safeguard tunnel construction.