On the 15th, during the construction of the Sichuan Dujiangyan to Siguniang Mountain (hereinafter referred to as "Du-Si") mountain rail transit project undertaken by China Railway Tunnel Group Co., Ltd., the "Shuguang" shield machine successfully broke through the ground at Puyang Station, marking the smooth completion of **China's first shield tunnel for a mountain rail transit project**.

　　The Du-Si mountain rail transit project starts at Dujiangyan Station, the hub station of the Chengdu-Guanxian high-speed railway, and ends at Siguniang Mountain Town in Xiaojin County, Aba Prefecture. The main line is 123 kilometers long, with a bridge-tunnel ratio exceeding 98%. The Yongfeng Station to Puyang Station section completed this time is 3,261 meters long and was excavated using an earth pressure balance shield machine with an excavation diameter of 9.73 meters.

　　The entire section lies beneath the busy Yong'an Avenue. It not only had to contend with long-distance excavation through strata with high water content, high permeability, high cobble content, and oversized boulder layers, but also had to overcome the impact and wear of large-diameter cobbles and boulders on the cutterhead and cutters, as well as multiple challenges such as water ingress, muck surges, and ground settlement. It is regarded by industry insiders as the "limit stratum for shield construction."

　　During construction, the project team of China Railway Tunnel Group actively formulated scientific construction plans to tackle the extreme strata. They invited several well-known domestic experts to hold multiple consultation and demonstration meetings, and organized project technical personnel to convene technical seminars and technical review meetings. At the same time, the construction team established the "Mu Yongqi Shield Extreme Stratum Research Base Craftsman Studio," focusing closely on key and difficult issues in the construction process to carry out technical research, providing strong technical support for the project to successfully complete the excavation task.

　　Ultimately, over more than 900 days, the construction team overcame multiple difficulties including complex and variable geological conditions and harsh construction environments, achieving important breakthroughs with the 9.7-meter-class large-diameter earth pressure shield machine in sandy gravel strata: 7.5 rings (12 meters) excavated per shift, 15 rings (24 meters) per day, and 321 rings (513.6 meters) per month. They completed the task objectives with high quality and smoothly achieved tunnel breakthrough.