Country's longest metro loop line now fully open in Wuhan with 37 stations

China's longest metro loop line opened in full on Thursday in Wuhan, Hubei province, linking seven central districts and two major railway stations and offering passengers more travel options across the river-divided city.

The 59.9-kilometer Line 12, recognized by the China Association of Metros as the country's longest metro loop, has 37 underground stations. A full circuit takes about 96 minutes, and passengers can transfer to 11 other operating metro lines.

The opening of the 24.64-km second phase completed the loop after the first section began operations on May 1. The line connects residential neighborhoods and business districts with Hankou and Wuchang railway stations.

Wuhan is divided by the Yangtze and Hanjiang rivers into the urban areas of Hankou, Wuchang and Hanyang. To connect them, Line 12 passes beneath the Yangtze twice and the Hanjiang once, presenting construction teams with challenges including high water pressure, water-bearing sand and complex ground conditions.

One of the most challenging sections was the roughly 4-km-long tunnel between the Science Park and Danshuichi stations. According to the State-owned Assets Supervision and Administration Commission of the State Council, it is the country's longest metro tunnel crossing the Yangtze.

Built by China Railway 14th Bureau Group, the tunnel provides a direct metro connection between Qingshan and Jiang'an districts on opposite banks of the river.

Engineers had to contend with high water pressure and changing geological conditions along the route. Dense sand accelerated wear on cutting tools, while mudstone would clog the tunnel-boring machine's cutting head. Construction teams adapted the equipment and continuously monitored conditions to minimize the impact on river embankments, railway lines and other nearby infrastructure.

Elsewhere, teams faced the challenge of building new tunnels close to existing transport facilities while keeping them in operation.

On a section built by China Railway 11th Bureau Group, new tunnels were excavated beneath elevated roads, an existing railway and three operating metro lines. The work involved tunneling through sand containing groundwater, with the closest point between a new tunnel and an existing metro tunnel measuring just 2.65 meters. Eight tunnel-boring machines were deployed at different locations along the section.

Teams monitored ground movement in real time and used carefully controlled excavation and grouting to minimize disturbance to the surrounding ground.

Ni Zhengmao, who oversees shield tunneling for the company responsible for the construction and operation of Wuhan Metro Line 12, said launching and receiving tunnel-boring machines were among the highest-risk stages of construction. Teams carried out checks on ground reinforcement, entrance seals and monitoring arrangements to manage the risks.

Beyond expanding the city's transport network, the completed line introduces a high level of automation into daily operations.

According to the train design team at CRRC Changchun Railway Vehicles, trains can automatically start up, conduct self-checks, leave the depot and return after completing service. Operators can also take remote control of trains from the control center.

"From the design stage, we built full automation into every operating scenario," said Xiong Chaohui, deputy chief engineer at China Railway Siyuan Survey and Design Group and the project's chief designer.

The design team said the system was tailored to the loop line's heavy passenger flows, frequent departures and closely timed transfers. Designers refined 11 automated operating scenarios, and the system can adjust departure intervals during peak periods.

Automation also extends to equipment maintenance. A centralized monitoring center integrates information from trains, signaling and communications systems, as well as platform doors, enabling staff members to monitor equipment and diagnose faults. Remote restart devices allow technicians to restart equipment without having to travel to the site.

"In the past, when equipment had a problem, maintenance staff members had to take a taxi to the site in the middle of the night to restart it," said Dong Ming, an operations technician.

"Now we have remote restart devices at the maintenance center and equipment hubs along the line," he said.

Contact the writers at luowangshu@chinadaily.com.cn