On the morning of October 20

With the successful reception of the "Innovation" shield machine

Constructed by China Railway 14th Bureau Group

The left-line shield tunnel of the Nanjing Jianning West Road River Crossing Project

Was successfully completed

Marking another important breakthrough in the construction of Nanjing's Yangtze River tunnel

Laying a solid foundation for the double-line breakthrough by the end of this year

The Jianning West Road River Crossing Project is located between the Yangtze River Bridge and the Yangtze River Tunnel. It starts from Jiangbei Avenue, runs south along Xingpu Road, crosses the Jinpu Railway, passes under the Yangtze River and Jianning Road, and ends at Jinchuanhe West Road, with a total length of 8.4 kilometers. The left-line shield tunnel is about 2,349 meters long, with a shield excavation diameter of 15.07 meters and a segment outer diameter of 14.5 meters. It is designed as a dual-tube, 6-lane urban expressway standard.

The largest risk source of the entire line

No domestic experience to draw on

The construction of the left-line shield tunnel of the Jianning West Road River Crossing Project is extremely difficult. It is a river-crossing underwater tunnel in China where a large-diameter shield machine passes through a combination of complex geological conditions in one go, including strong permeable sand layers, soft-hard uneven composite strata, wide fault fracture zones, and fully weathered silty clay layers. It also needs to cut through the reinforced concrete anti-slide pile group of the south bank levee of the Yangtze River. It is currently one of the most difficult tunnel projects in the Yangtze River Basin and in the country.

★ The maximum water depth in the river-crossing section is 55 meters, with a maximum water and soil pressure of 7.7 bar, equivalent to bearing the weight of 8 elephants per square meter.

★ In the 310-meter fault fracture zone, the strata are soft at the top and hard at the bottom, with a maximum rock compressive strength of 147.6 MPa.

★ The minimum cover thickness at the riverbed is only 10.55 meters, less than 0.75 times the tunnel diameter.

★ The Yangtze River levee is adjacent to a deep channel, with deep water, steep slopes, and soft geology.

★ The shield machine cutting through reinforced concrete anti-slide pile groups is the first case in China, with no experience to draw on and extremely high construction risk.

Pioneering shield

Acting as pathfinder

By absorbing domestic and international experience in river and sea crossing shield tunnel construction, the builders conducted targeted research and design on the cutterhead type, cutter type, and pressure resistance of the shield machine.

The shield machine is equipped with a normal-pressure cutterhead, enabling safe and quick cutter replacement at the riverbed. It is equipped with a retractable main drive with a maximum stroke of 40 centimeters, greatly reducing the risk of cutter replacement at the riverbed. It is equipped with a fully automatic advanced drilling and grouting system to address construction risks in the riverbed fracture zone. The shield machine is equipped with and uses in-chamber telescopic cameras and a cutter load monitoring system, laying a solid foundation for the smooth progress of the project.

The strongest brain diagnoses

Formulating detailed construction plans

To overcome the biggest challenge in the construction of this river-crossing tunnel—cutting through the reinforced concrete anti-slide pile group of the levee—the project department of China Railway 14th Bureau Group formulated detailed construction plans. On December 9, 2022, the Nanjing Public Engineering Construction Center invited the Nanjing River Crossing Channel Construction Technical Expert Group to hold a working meeting to evaluate the construction plan. Eleven renowned experts, including Academician Qian Qihu of the Chinese Academy of Engineering, conducted in-depth inquiries and discussions on the plan and concluded that the plan for the "Innovation" shield machine to cross the south bank levee of the Yangtze River was feasible. They required the participating units to summarize construction experience and conduct levee monitoring.

The "Innovation" shield machine successfully completed the crossing of the south bank levee, accumulating valuable experience for super-large-diameter slurry shield machines cutting through reinforced concrete piles. It set a construction precedent for a large-diameter shield machine in China cutting through a river levee anti-slide pile group for the first time, laying a solid foundation for the smooth progress of the project.

Since its launch in August 2021, after 26 months, the shield tunnel was successfully completed, achieving the feat of crossing the Yangtze River. The project has been rated as a national "Construction Safety Production Standardization Demonstration Site" and a 2022 Jiangsu Province Safe and Centennial Quality Engineering Demonstration Project, and has won the provincial safety demonstration site for three consecutive years.

Interior view of the completed tunnel

It is understood that the Jianning West Road River Crossing Project, as an important channel connecting the main city on the south bank and the national-level new area on the north bank, is of great significance for promoting Nanjing's river-embracing development, accelerating the construction of the Jiangbei New Area, enhancing the Yangtze River crossing capacity, alleviating traffic pressure in the main city, and continuously improving the regional road network system.