On the 16th, the only extremely high-risk tunnel in China's alpine region, defined by domestic tunnel experts as the "biggest challenge in China's alpine region"—the Aimin Tunnel on the Harbin-Mudanjiang Passenger Dedicated Railway—was successfully holed through. The tunnel overcame numerous challenges, and its innovative practices are worth learning from for tunnel construction in China's alpine regions.
Li Baocheng, project manager of the Harbin-Mudanjiang Passenger Dedicated Railway Project Department of China Railway 22nd Bureau Group, introduced that the 292.995-kilometer Harbin-Mudanjiang Passenger Dedicated Railway is the northernmost "horizontal" line in China's "eight vertical and eight horizontal" high-speed rail network and an important part of the rapid passenger transport network in Northeast China. At the same time, the Harbin-Mudanjiang Passenger Dedicated Railway forms a major transport corridor from Suifenhe, a port in eastern Heilongjiang Province, to Manzhouli, a port in the Inner Mongolia Autonomous Region, and is very important for building the Eurasian Continental Bridge.
When high-speed trains on the Harbin-Mudanjiang Passenger Dedicated Railway enter the urban area of Mudanjiang, they will enter the 2,940-meter-long Aimin Tunnel in the suburbs, and then ascend to the surface when approaching Mudanjiang Station, generally forming a "V" shape, thereby reducing the impact of the high-speed rail opening on the urban environment and people's lives. This also results in a height difference of 41.8 meters in the tunnel, with slopes of 14.8‰ and 18‰ on both sides, while the slope of high-speed rail lines is generally 5‰.
Xu Song, tunnel captain of the Harbin-Mudanjiang Passenger Dedicated Railway Project Department of China Railway 22nd Bureau Group, said that the Aimin Tunnel is located in China's cold region, with an extreme minimum temperature of minus 35 degrees Celsius, and faces technical challenges such as frost heave prevention, snow damage prevention, and winter construction. The entire line passes through multiple "loose sedimentary layers," "Tertiary mudstone and sandstone" and other strata, with Grade V and Grade VI surrounding rock accounting for 95% of the length, and is known as a "geological museum in the alpine region." In particular, between the tunnel entrance and the No. 1 inclined shaft, and between the No. 1 and No. 2 inclined shafts, the interbedded sandstone and mudstone sections of more than 470 meters are geologically weak, and even mountain creep occurred, causing severe settlement and convergence of the tunnel arch, continuous collapses, and construction on site had to stop several times.
The Harbin-Mudanjiang Passenger Dedicated Railway Project Department of China Railway 22nd Bureau Group established a technical research team, adopting "anti-slide pile protection + surface grouting" for the creeping geology at the tunnel entrance section, and implementing full curtain grouting for the interbedded sandstone and mudstone sections between the No. 1 and No. 2 inclined shafts, thereby improving the self-stability of the soil layer and ensuring safe excavation.
After an in-depth site survey, tunnel design master Shi Yuxin believes that the proportion of soft rock in the Aimin Tunnel is rare in China, especially with large deformation and many control points. The technical research team of the Harbin-Mudanjiang Passenger Dedicated Railway Project Department of China Railway 22nd Bureau Group, together with relevant experts, overcame challenges such as alpine cold, shallow cover, biased pressure, water-richness, and large span, and its innovative practices are worth learning from for tunnel construction in China's alpine regions.