After 843 days and nights of arduous efforts, the tunnel section from Dujiangyan to Yongfeng Station of the Dujiangyan to Siguniang Mountain Mountainous Rail Transit (hereinafter referred to as "Du-Si Mountainous Rail Transit") was successfully holed through recently. The section is 6.7 kilometers long and was excavated simultaneously by two shield machines, "Shuguang" and "Shuxin"; it is the most difficult shield-driven section on the entire line. The section has a high proportion of cobbles and boulders of large size, which posed challenges for shield machine operation such as frequent cutterhead jamming, cutter cracking and detachment, and screw conveyor jamming and shaft breakage, and is therefore also known in the industry as a "shield machine excavation forbidden zone."

Formed tunnel

In response to the special geological conditions and excavation environment along the Du-Si Mountainous Rail Transit, the shield machine designer CCCC Tianhe carried out extensive targeted and adaptive design in the early stage. The "Shuxin" and "Shuguang" shield machines responsible for excavation adopted large-opening cutterheads, belt-type screw conveyors, heavy-duty ripping cutters, and high-torque, high-thrust combinations. During excavation, even cobbles weighing more than an Asian elephant could be "swallowed" in one bite. In contrast, conventional shield machine excavation modes need to crush cobbles before slowly "swallowing" them, resulting in slower excavation efficiency and the need for frequent replacement of shield machine cutters.

Giant cobbles excavated. According to Zhou Jun, Deputy General Manager and Chief Engineer of CCCC Tianhe, as the developer of the shield machines for the Du-Si Mountainous Rail Transit project, the project team worked in close collaboration with relevant units to address the excavation challenges of extremely water-rich strata with large-diameter boulders and isolated rocks, carrying out a series of technical research and scientific and technological innovation, and achieving 8 QC (quality control) results, 5 utility model patents, and 10 invention patents, providing reference for future excavation in similar geological environments.

The Du-Si Mountainous Rail Transit project is the country's first high-altitude mountainous rail project using rack rails as running tracks, and is also a key rail transit tourism pilot poverty alleviation project in Sichuan Province. It starts at Dujiangyan Station of the Chengdu-Guanxian High-Speed Railway and ends at Siguniang Mountain Town in Xiaojin County, Aba Prefecture. The line is 123.18 kilometers long with a designed operating speed of 120 kilometers per hour; most sections are viaducts or tunnels, with bridges and tunnels accounting for more than 98%.

It is reported that once the project is completed, it will connect the rich tourism resources of western Sichuan with the Chengdu Plain as a whole, not only allowing passengers to enjoy the scenery of the western Sichuan Plateau by rail transit and promoting the transformation and upgrading of natural resource advantages into economic advantages, but also providing a guarantee for local people along the line to become better off and increase their incomes, which is of great significance for driving economic development along the line.