On June 18, new progress was reported in the Ningwu Railway capacity expansion and renovation project: the roof slab of the shield launching shaft for the Nanjing South Tunnel was capped, marking that the conditions for shield machine launching have basically been met. Next, the "Ningwu" shield machine will enter the site for assembly, and the 2.4-kilometer "underground crossing" has officially entered the countdown.

It is understood that the Nanjing South Tunnel is a controlling project for the entire Ningwu Railway capacity expansion and renovation project, with a total length of 14.442 kilometers. It is a single-tube single-track tunnel designed for a speed of 120 kilometers per hour. The shield-driven section of the tunnel is about 2.4 kilometers long. The shield machine will be launched from the Meixiang Road working shaft in Yuhuatai District and will terminate at the existing Hanfu Mountain Tunnel in Jiangning District for reception.

In view of the characteristics of the shield section, including water conditions and complex surface and underground environments, the project adopts the "Ningwu" shield machine, with targeted improvements in cutterhead structure, cutter arrangement, excavation control, shield tail detection and other aspects, laying a solid foundation for the smooth progress of the project.

The shield machine has an excavation diameter of 9.33 meters, a total length of 132 meters and a weight of about 1,375 tons. It applies multiple advanced intelligent technologies such as a visualized excavation chamber system and a shield tail brush wear detection system, and is equipped with wear-resistant inserted-tooth disc cutters, a single-pipe single-pump muck conditioning system, and a continuous belt conveyor, which will effectively improve the efficiency and quality of shield tunneling.

The shield-driven section of the project successively passes beneath Nonghua River and the Airport Expressway, crosses over Metro Line S1, runs parallel with Metro Line S3 over a long distance, and passes beneath the Qinhuai New River and the existing Beijing-Shanghai High-Speed Railway tunnel at Hanfu Mountain. Among these, the crossing beneath the Qinhuai New River is the most technically difficult, with the shallowest cover soil only 2.6 meters, the shallowest cover soil layer encountered in a domestic shield project to date.

Because the shallowest cover soil is less than one-third of the shield diameter, the contractor will use backfilled concrete at the riverbed to reinforce the cross-section, and at the same time add a reinforced concrete inner lining inside the tunnel to meet the anti-floating requirements of the tunnel underwater.

It is understood that before shield tunneling, the contractor will test the compactness and integrity of the backfilled and poured concrete at the riverbed, and tunneling will proceed only after the quality is qualified, so as to ensure the safety of shield construction and the Qinhuai New River.

The main line of the Ningwu Railway capacity expansion and renovation project is about 102.2 kilometers long. The project starts from Nanjing East Marshalling Station in the north, passes through Qixia District, Xuanwu District, Qinhuai District, Yuhuatai District and Jiangning District of Nanjing, enters Ma'anshan City of Anhui Province, passes Dangtu County into Wuhu City, and ends at Wuhu East Station.

Among these, electrification renovation is implemented for the section from Nanjing East Marshalling Station to Cangbomen and for the passenger train connecting line from Mennan Village to Nanjing Station; the existing railway from Cangbomen to Guxiong is relocated; and electrification renovation and the conversion of level crossings to grade separations are implemented for the section from Guxiong to Wuhu East.

The relocation of the line in the urban section of Nanjing (from Cangbomen to Guxiong) will effectively eliminate the safety risks of railway level crossings in the urban area and resolve the current problems caused by the original line passing through the city, such as severing the city, noise disturbance, pollution emissions and traffic congestion. Traffic on many major and secondary urban roads will no longer be affected by the railway, greatly improving traffic accessibility.

After the project is completed and put into operation, it will further optimize the layout of the regional railway network and is of great significance for implementing the concept of "ecological priority and green development," accelerating the upgrading and adjustment of the industrial structure in areas along the line, optimizing the spatial layout of urbanization, and enhancing the flexibility of the railway network.