How China ‘saved’ a $50 million machine stuck underground

The problem initially arose in February 2023 during the construction of the 6.4 km Jiangyin-Jingjiang road tunnel beneath the Yangtze River. The project was carried out using a 16 m diameter shield tunneling machine, worth 50 million USD. However, while digging at a depth of 54 m, it suddenly stopped working.

The incident occurred just below the main traffic channel of the Yangtze River. The water pressure at this location in the ground reaches nearly 0.76 megapascals, acting on the machine’s shield with a force of about 76,000 kg per m2. In this condition, the machine cannot reverse and cannot be safely dismantled for recovery or on-site repair.

The situation is extremely difficult, with the risk of turning a large-scale tunneling project into a disaster. The engineering team faced two options: abandon the machine and accept losses, completely redesign it, or cancel the tunnel project. Either option would lead to years of delay and cause considerable trouble for all parties involved.

After extensive discussions led by members of the Chinese Academy of Engineering, the project team decided on a third option, an unprecedented “rescue” plan: Deploy a second shield tunneling machine that digs from the opposite direction and meets underground, beneath the Yangtze River.

“The biggest challenge is ensuring the new tunnel boring machine navigates to the correct position in a high-pressure soil environment with lots of water and flowing sand,” expert Yao Zhanhu at China First Highway Engineering told the publication. Science and Technology Daily.

Six months after the incident, the second tunneling machine began to advance slowly from the opposite side, towards the stuck machine. To achieve the required accuracy, the project team developed a real-time visual navigation system. The machine’s cameras and sensors collect tunneling and environmental data, allowing for comprehensive monitoring.

On July 21, 2024, the two machines were successfully paired below the Yangtze River, almost completely aligned. The horizontal deflection at the junction is 0 mm, the vertical deflection is 2 mm – well within the 10 cm design tolerance and exceeding all expectations.

After the first successful step, the project team needed to freeze the joint area to keep it stable and avoid collapse and flooding of the tunnel. Expert Chen Xiangsheng from the Chinese Academy of Engineering, proposed the method of grouting first, freezing later. Workers drilled 363 pipes from inside tunneling machines to pump grout into the ground, then installed the freezing pipes, creating a 3.9 meter thick wall of frozen soil that cooled to an average of -13 degrees Celsius.

The final important step is to dismantle the two giant tunnel boring machines. Due to being stuck head to head, they cannot be pulled out intact. Workers separate each machine into about 2,000 parts, each weighing one ton. Because the outer layer has frozen, all dismantling and handling steps must be done manually to avoid temperature imbalance. During this process, concrete is injected into the outer rim of the tunnel for long-term stabilization.

On March 26, 2025, two years after the incident, the main structural lining at both ends of the tunnel was completely connected, and construction teams from both directions also met. At the end of November last year, the underwater connection section of the Jiangyin – Jingjiang road tunnel under the Yangtze River was officially completed.

The tunnel is expected to fully open mid-year. Built to dual 6-lane highway standards, this will be the largest diameter tunnel in China with the highest water pressure resistance upon completion.

Interesting Engineering According to the assessment, the feat of Chinese engineers shows that “rescuing” a project having major problems with tunneling machines deep underground, even below rivers, is completely feasible. Experience from troubleshooting can be applied to future projects such as undersea tunnels, subway systems and structures in high-risk geological environments.