The No. 12 section of Metro Line 1, constructed by China Railway Eleventh Bureau Group, includes three shield tunnel sections: Changlepao–Wanshou Road Station, Wanshou Road–Tonghuamen Station, and Tonghuamen Station–Kangfu Road Station. This section also features two mined tunnels and one ventilation shaft, with a total length of 3,748.85 double-track meters. Construction officially began on March 18, 2009, with an anticipated completion date in early 2012.

　　This tunnel boring machine (TBM) started at Changlepō Station, traveling east to west along Changle Road. It passed through Wanshou Road Station and Tonghuamen Station before reaching Kangfu Road Station, where it was dismantled and lifted out. The two TBMs crossed the underground tunnel twice each and went through two stations (Wanshou Road Station and Tonghuamen Station), requiring a total of four launching operations and four receiving operations—resulting in frequent shifts in construction procedures. Meanwhile, the initial support work for the F5 underground tunnel was successfully completed on June 15, and secondary lining construction is now underway. Additionally, the ventilation shaft for the Wanshou Road–Tonghuamen Station section has already finished setting up site barriers, conducting pipeline surveys, and undergoing expert review of the proposed plan.

　　This project section features complex geological conditions and a challenging surrounding environment, presenting numerous construction difficulties. Specifically, the 300-meter-long full-face sand-gravel stratum and the 900-meter-long semi-face sand-gravel section between Changlegpo Station and Wanshou Road pose significant challenges for shield tunneling—this is the first time such formations have been encountered in shield construction within the Xi'an region. Key issues during construction include optimizing muck conditioning to reduce thrust and torque on the TBM, thereby minimizing wear on the cutterhead and cutting tools caused by the abrasive sand-gravel layers. Additionally, effectively managing ground settlement in these sand-gravel strata will be critical to overcoming this hurdle. Furthermore, the section from Wanshou Road through Tonghua Gate to Kangfu Road passes through localized areas characterized by collapsible loess soil, where the groundwater level lies just 3–5 meters above the tunnel crown. Ensuring the watertight integrity of the TBM’s tail seal during construction is essential to prevent water loss and subsequent ground subsidence—a major focus of this project. Lastly, the shield tunneling route traverses several key infrastructure elements, including the Huashan Factory Dedicated Railway Bridge, a buried sewage pipe (2000 mm in diameter) at a depth of 20 meters, as well as close proximity to structures like the Huanghe Hot Spring Residential Complex, the three-story China Electronics Materials Northwest Company building, the Wanshou Road Pedestrian Overpass, the Wool Sweater Wholesale Market, the North Second Ring Elevated Bridge, and the Xijing Hospital Pedestrian Overpass. Alongside these obstacles, the project must carefully manage potential ground and structural settlements, as failure to do so could jeopardize the entire project’s success.

　　Currently, the left tunnel section has completed 200 meters of full-face shield tunneling through the gravelly sand strata. All performance indicators of the tunneling machine remain normal, and ground settlement has stayed well within the design tolerances. Throughout the construction process, the project team conducted extensive spoil-conditioning tests and meticulously analyzed and summarized the tunneling parameters. As a result, a reliable method for advancing through the gravelly sand layers has been successfully established. Today, the daily tunneling rate has reached an impressive 12 rings per day, enabling fast and stable progress through this challenging ground condition—and laying the groundwork for efficient right-tunnel shield construction. Meanwhile, this experience also provides invaluable data for future shield tunneling projects in similar gravelly sand formations across the Xi'an region.