On August 30, the Zhenjiangguan–Huangshengguan section of the Sichuan–Qinghai Railway officially opened for operation. Once in service, the line will greatly facilitate travel for people of all ethnic groups along the route, drive economic and social development in the areas it passes through, and be of great significance for safeguarding ethnic unity and supporting the implementation of the Western Development Strategy in the new era.

The Zhenjiangguan–Huangshengguan section of the Sichuan–Qinghai Railway lies in the high-mountain and deep-valley terrain on the eastern edge of the Qinghai–Tibet Plateau, with elevation rising from 2,503 meters at Zhenjiangguan Station to 3,156 meters at Huangshengguan Station. It crosses numerous mountain ranges including the Motianling, and the complex geological conditions along the route made construction highly challenging.

Since construction began in March 2011, the project has completed seven tunnels including the Desheng Tunnel and erected 21 bridges including the Yuanbazi Minjiang Double-Track Extra-Large Bridge, ensuring the project was completed on schedule.

The breakthrough site of the Desheng Tunnel (photo courtesy of Chengdu Railway Bureau)

Among them, the Desheng Tunnel is widely recognized within the industry as one of China's most difficult mountain-crossing tunnels. How important is the Desheng Tunnel, and how was it excavated and holed through meter by meter?

The Desheng Tunnel has a total length of 22,923 meters and is Asia's longest single-tube double-track railway tunnel. Selecting the tunnel portal posed enormous difficulties—it lies in the Minjiang River gorge area, where the terrain consists of deeply incised high mountains and valleys. In addition, the effects of several earthquakes in recent years have been pronounced, and adverse geological features such as dangerous rockfalls, debris flows and landslides are very densely distributed along the tunnel route.

Construction of the Desheng Tunnel began in 2014, and after 2017 large deformation of soft rock was encountered. This problem also occurs in other tunnels, but it was especially severe in the Desheng Tunnel: of the tunnel's 22 kilometers, more than 7 kilometers experienced large deformation. During construction, the proportion of large deformation across the whole tunnel reached as high as 32.6%, and problems such as face collapse, mud bursts and water inrushes occurred more than 300 times in total. The Desheng Tunnel is therefore widely recognized within the industry as one of China's most difficult mountain-crossing tunnels.

A high-speed train takes only 7 minutes to pass through the tunnel, yet the construction period lasted as long as 3,540 days. The Desheng Tunnel has complex geological conditions, a large proportion of weak surrounding rock, a significant group-cavern effect, strong groundwater influence, high technical difficulty and great construction difficulty... The rock mass in the tunnel is extremely weak and fractured, making it akin to "boring a hole in tofu."

The Desheng Tunnel features what is currently the "largest in Asia and largest in China" tunnel disaster-prevention and rescue station. Building a tunnel within a tunnel also represented a breakthrough in technological innovation. The rescue station has a three-level structure of "upper level for smoke exhaust, middle level for evacuation, and lower level for withdrawal (escape)," and as a whole consists of a group of 35 caverns with a length of more than 3,100 meters, making it large in scale and complex in structure.

(Photo courtesy of Chengdu Railway Bureau)

As the controlling project of the entire Sichuan–Qinghai Railway, the construction of the Desheng Tunnel has provided valuable experience for railway construction in plateau and mountainous areas in China and even around the world. It is understood that the Sichuan–Qinghai Railway is an important component of the Lanzhou–Xining–Guangzhou corridor in China's "Eight Vertical and Eight Horizontal" high-speed rail network. The line starts at Chengdu East Station and passes through Chengdu City and the Aba Tibetan and Qiang Autonomous Prefecture in Sichuan Province, Gannan Tibetan Autonomous Prefecture in Gansu Province, and Huangnan Tibetan Autonomous Prefecture, Haidong City and Xining City in Qinghai Province, connecting to Xining Station. The main line has a total length of about 836 kilometers and a design speed of 200 kilometers per hour, and is a Grade I double-track railway of the national railway network.