Recently, Bid Section 13 of the Shanghai Municipal Railway Airport Link Line, invested in and constructed under the responsibility of Shanghai Shentie and built by Shanghai Construction Group, has reached a new construction milestone. As the "Jianshun" shield machine for the long right-line section from Pudong Airport Terminal 1 & 2 Station to Pudong Airport Terminal 3 Station fully exited the lowest point of the excavation axis, it marked that Bid Section 13 of the Airport Link Line has officially entered the shield tunneling slope-changing stage.

The Bid Section 13 project is located in Zhuqiao Town, Pudong New Area, with a total section length of about 5.7 kilometers, including the Pudong Airport working shaft, the underpinning of the south turnaround ramp bridge piers, the section tunnel and related auxiliary works. Among them, the section from Pudong Airport Terminal 1 & 2 Station to Pudong Airport Terminal 3 Station has left and right lines each about 3.03 kilometers long; the tunnel has a "V"-shaped slope, with a tunnel crown depth of 22.11 meters to 51 meters, and two cross passages. This is also currently the deepest shield tunnel section in Shanghai.

The section is constructed with two 9-meter-class slurry pressure balance shield machines. "Jianshun" is responsible for the dual-line tunneling from Pudong Airport Terminal 1 & 2 Station to the Pudong Airport working shaft and the right-line tunneling from the Pudong Airport working shaft to Pudong Airport Terminal 3 Station. "Jiansheng" is responsible for the left-line tunneling from the Pudong Airport working shaft to Pudong Airport Terminal 3 Station. As of now, the left-line and right-line sections have completed 1,201 rings and 705 rings, respectively.

Under the overall deployment and advance organization of Shanghai Shentie, the project team overcame multiple technical challenges. During shield tunneling, the machine needed to pass beneath the Pudong Airport flight area over a long distance. How to ensure the safety of numerous buildings and structures, including airport taxiways, satellite hall high-pole light towers, the satellite hall, the airport APM tunnel (shield section), and overhead pipeline supports, was a major difficulty in this construction. The project team preemptively increased the slurry pressure of the shield machine so that the ground and buildings/structures ahead of the shield machine always maintained a slight tendency of heave, effectively reducing disturbance to the surrounding soil. At the same time, the grouting volume was increased to 160%, and cement was added to the simultaneous grouting to reduce the initial setting time of the simultaneous grout, so that a waterproof lining was formed outside the tunnel in a timely manner. This not only ensured the waterproof performance of the tunnel but also provided a strong guarantee for safety and stability during the shield machine's crossing.

The ultra-deep, ultra-long-distance full-face sand layer was another challenge in shield tunneling. The shield machine needed to tunnel about 1,900 meters in the ⑦2 full-face sand layer; such a long-distance crossing is the first of its kind in the domestic engineering field. After the tunneling stratum changed from a clay layer to a sand layer, the project team promptly adjusted the slurry treatment equipment according to the characteristics of the sand layer and improved the indicators of the slurry circulation fluid to ensure the stability of all indicators during advancement. At the same time, deviation correction control was carried out according to the principle of "frequent measurement and frequent correction, small-angle correction" to ensure the smooth tunneling of the shield machine in the ultra-deep, ultra-long-distance full-face sand layer.

The maximum depth of the tunnel crown in the section from Pudong Airport Station to the planned terminal station reaches 51 meters, placing high demands on the shield machine's thrust. The project team used a new type of thixotropic slurry with excellent lubricity and stability to significantly reduce the friction resistance on the outer side of the shield machine and meet the thrust requirements. In addition, three sets of cylinders were added at the bottom of the shield machine to meet the requirements for upward deviation correction and self-rescue when the machine body is at the lowest point.