Recently it was learned that the last single-track section of the eastern extension of Nanchang Metro Line 2 will achieve breakthrough on April 16, which means that all three extension lines of Nanchang Metro have achieved full tunnel breakthrough, laying a solid foundation for subsequent construction goals such as track connection, power connection, and no-load trial operation.

　　According to reports, the eastern extension and northern extension of Nanchang Metro Line 1 and the eastern extension of Line 2 total 31.75 kilometers, with 19 stations and 19 sections, passing through four major administrative districts: Nanchang Economic Development Zone, Honggutan District, Qingyunpu District, and Qingshanhu District. The project started construction in September 2021 and is scheduled to be completed and opened to traffic by the end of 2025. At present, the three extension lines achieved tunnel breakthrough on September 28, 2023, March 25, 2024, and April 16, 2024, respectively.

　　The comprehensive tunnel breakthrough of the three extension lines of Nanchang Metro this time will further connect four major comprehensive transportation hubs: Changbei Airport, Nanchang West Railway Station, Nanchang Railway Station, and Nanchang East Railway Station, and a more convenient transportation transfer system will follow. At the same time, as an important part of continuously improving the "ring + radial" urban rail network and building a modern comprehensive transportation system, it plays an important role in supporting the construction of "one hub and four centers."

　　It is understood that although the mileage of the three extension lines of Nanchang Metro is not long, there are no shortage of "hard bones." Taking the eastern extension of Line 2 as an example, the sections along the line need to pass beneath 76 old houses that are long-standing, complex in structure, and densely located, and there are more than 100 risk sources above the tunnels, such as large-diameter and old pipelines, showing the difficulty of construction.

　　What does overcoming difficulties rely on?

　　——It relies on technology. According to reports, all 19 sections of the three extension lines adopted "Nanchang-made" shield machines, with 11 used on the eastern extension of Line 2 alone, truly realizing the use of equipment manufactured by Nanchang enterprises to build Nanchang Metro. At the same time, it also created a result of 31 months from construction start to tunnel breakthrough for the three extension lines, 22.5% faster than the 40 months of Line 4, setting a new record for the fastest tunnel breakthrough in Nanchang Metro construction.

　　Fengxia Station—Hufang Station is the section with the smallest radius and the largest number of houses passed beneath on the eastern extension of Line 2, and the "Nanchang-made" shield machine was used to complete the excavation task. Before shield launching, the construction party noticed that this section was in reinforced strata, and using a conventional cutterhead carried risks such as slow excavation speed and easy ground settlement. For this reason, we carried out targeted selection of the shield machine. After multiple expert demonstrations, it was decided to add 6 edge disc cutters on the basis of the original full-face tearing cutters to accelerate the speed of cutting hard strata, better control the amount of excavated soil, manage various risks, and achieve fast and stable shield excavation. Thanks to the realization of "Nanchang-made, Nanchang-used" for the shield machine, it took only 1 month from assembly, lifting, commissioning, and rolling off the line, winning more time for subsequent construction.

　　The Hufang Station—Nanchang East Railway Station section faced many difficulties and overlapping risks. The shield machine not only had to pass through "upper soft and lower hard" "washboard"-type strata, but also had to excavate in small-clearance, long-distance overlapping tunnels. To this end, the construction party accurately identified the problems and solved them by installing steel supports in the formed tunnel below and injecting cement grout to reinforce the overlapping section, ensuring the safety of the upper and lower tunnels during excavation.

　　——It relies on innovation. In order to efficiently transport about 200,000 cubic meters of muck, the project department of the Changbei Airport Station—Huangdun Station (intermediate ventilation shaft) section "invited" a belt conveyor shield muck transport system, which was the first of its kind in Nanchang Metro construction, and the vertical belt conveyor depth of 25 meters is currently the deepest depth of a subway shaft belt conveyor in China. The entire belt transmission system consists of a horizontal belt conveyor and a vertical belt conveyor. The muck cut by the shield machine cutterhead falls onto the horizontal belt conveyor, and then the muck is unloaded through a hopper into the "pockets" on the vertical belt conveyor, and then quickly transported to the ground. Thanks to the uninterrupted operation of the belt conveyor, the muck removal efficiency increased by more than 100%, and the number of excavation rings per day also rose from 7 at the beginning to 20. At the same time, later maintenance is simpler, and it also avoids the dangerous operation of lifting and transporting muck thousands of times.

　　In order to ensure that the shield machine is received smoothly at the existing operating Xinjia'an Station, the project department, after multiple expert "consultations," adopted the "freezing method + steel sleeve" reception method, which was also the first of its kind in Nanchang Metro construction. Simply put, after the shield machine reinforces the strata through freezing, it safely enters the closed pressure-maintaining steel sleeve, and finally the shield machine is lifted out of the steel sleeve, thus completing the entire reception process. This innovative move not only avoided problems such as surface settlement and segment floating in the section, but also ensured the safety of surrounding houses and the existing operating line.

　　——It relies on management. The construction of all three extension lines of Nanchang Metro achieved the goal of "three zeros" for accidents and incidents. How can such high safety control standards be achieved when working in complex underground environments?

　　This is due to Nanchang Rail Transit Group's promotion of the transformation of safety management from "passive emergency rescue" to "active prevention," creatively proposing the "standard diagram" risk control method, establishing an information-based, visualized remote real-time monitoring system for major risk source control measures, and successfully achieving the "three zeros" for accidents and incidents. According to reports, since the implementation of diagram-based control, shield and foundation pit construction control has achieved obvious results, and the number of single warnings dropped from 68 in 2018 to 7 in 2023, a decrease of 89.7%.

　　At the same time, the Civil Engineering Key Technology Research Center independently developed the "intelligent shield automatic excavation system," enabling shield excavation operations to move from "manual-based, intelligent-assisted" to "intelligent-based, manual-assisted." For example, thanks to this intelligent system, the shield machine successfully passed through the widest water area working face encountered in Nanchang Metro construction—the Yaohu East Station—Yaohu West Station section—and achieved automatic advancement, automatic pressure maintenance, and automatic deviation correction during excavation, with an error rate far lower than manual operation, greatly improving overall construction efficiency, construction standardization level, and formed tunnel quality.

　　It is worth mentioning that Nanchang Metro has carried out scientific research on key and difficult issues in different fields. The scientific research results have been appraised by multiple academicians and have reached the international advanced level as a whole, with some reaching the international leading level. These new construction methods and new processes have been widely applied in the construction of the extension lines, not only effectively reducing the number of warnings for stratum deformation and settlement, but also overcoming problems such as mud cake formation on the shield cutterhead and screw conveyor gushing, providing hard support for the fast and stable construction of the Nanchang Metro extension lines.