476-foot-long machine to dig deepest railway tunnel beneath Yangtze River

China has finished building a large shield tunneling machine for Nanjing’s first high-speed railway tunnel under the Yangtze River. This marks a big step forward for the underwater rail project. The machine was made in Hangzhou, Zhejiang Province, and China Railway Group said it was recently rolled off the production line on Sunday. Giant machine built for deep tunneling The machine, called “Linghang,” is a slurry balance shield type. It is 13.72 meters wide (about 45 feet) and 145 meters long (about 476 feet). China Railway Engineering Equipment Group and China Railway Tunnel Group worked together to develop the machine for this challenging cross-river project. Its large size allows it to dig a single tunnel that will hold two high-speed railway tracks. The equipment will face challenging geological and underwater conditions as it advances beneath the Yangtze River. Engineers have therefore incorporated a double-layer shell into its design. Outer shell will stay underground The double-layer structure is designed to simplify the machine’s recovery after tunneling. Once excavation is finished, crews can remove the backup system and inner shield while leaving the outer shell behind as permanent tunnel support. This approach is expected to make dismantling safer in confined underground spaces. It can also reduce the complexity involved in recovering large sections of tunneling equipment after the excavation is complete. The design is particularly important for a project where the machines will eventually have to be dismantled deep underground after completing their work. Tunnel reaches 351 feet deep Nanjing’s first high-speed railway cross-river tunnel will form part of a railway passage measuring about 20.4 kilometers (12.7 miles), in total. The tunnel section will extend for approximately 14 kilometers (8.7 miles). A significant portion of the route will run beneath the Yangtze River bed. The tunnel will reach a maximum burial depth of 107 meters (about 351 feet), while facing water pressure of up to 1.07 megapascals. Those conditions make it the deepest and highest-pressure railway shield tunnel along the Yangtze River to date, according to the project information. Two slurry shield machines will excavate the cross-river section from opposite ends. The machines are planned to meet with high precision beneath the river crossing before being dismantled at a depth of about 30 meters (98 feet), below the floodplain on the Yangtze’s north bank. New rail link targets major bottleneck The completed tunnel is expected to strengthen rail connectivity across the Yangtze in Nanjing, where the river has long presented a major challenge for railway infrastructure. The project is also tied to the wider development of China’s Yangtze River Economic Belt, one of the country’s major economic regions. Its regional GDP has more than doubled over the past decade as authorities have increasingly emphasized ecological protection alongside economic growth. The new high-speed railway connection is expected to improve transportation capacity while supporting development along the river corridor. Get the latest in engineering, tech, space & science - delivered daily to your inbox.A versatile writer, Sujita has worked with Mashable Middle East and News Daily 24. When she isn't writing, you can find her glued to the latest web series and movies.