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Failure Left 16-Meter-Diameter Machine Almost Buried Under One of China’s Most Important Rivers, Forcing Engineers to Create Unprecedented Operation to Complete 6.4-Kilometer Tunnel
A tunnel boring machine valued at around $50 million became immobilized approximately 54 meters below the surface of the Yangtze River after a failure in its main system. Unable to remove the machine or perform conventional repairs at that point, Chinese engineers adopted an extreme solution: start digging from the opposite side with another giant tunnel boring machine and make the two machines meet beneath the river.
The operation took place during the construction of the Jiangyin-Jingjiang Tunnel in Jiangsu Province, one of China’s major underground roadway projects. The damaged machine measured 16.09 meters in diameter, about 140 meters long, and weighed around 5,000 tons, dimensions that made it nearly impossible to remove using conventional methods.
The plan required a second machine of similar size to traverse the remaining stretch toward the exact point where the first was stuck, navigating saturated soil under heavy water pressure. When the two machines finally met, the instruments recorded zero millimeters of horizontal deviation and only 2 millimeters of vertical difference.
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Tunnel Boring Machine Stopped After Traveling More Than 3 Kilometers
The machine involved in the incident was known as Juli No. 1. It began digging in April 2022 and advanced approximately 3.2 kilometers before suffering a failure related to the main bearing system, a critical component for the cutting head’s operation on February 8, 2023.
At the time of the halt, there were still about 1,725 meters left to reach the other end of the planned stretch. Thus, the issue did not occur near an exit, but in an area where removing, dismantling, or repairing the structure posed a much greater engineering challenge.
The position was also particularly critical. The tunnel boring machine was located beneath the main shipping channel of the Yangtze, about 27 meters below the riverbed and approximately 54 meters below the water surface, surrounded by layers of saturated and highly permeable sand.
The water pressure in that area reached approximately 0.76 MPa. Any unsuccessful attempt to open the machine or access certain parts could allow a sudden influx of water and sediments, jeopardizing not only the equipment but also the entire tunnel already constructed behind it.
Removing the Machine or Drilling a Well in the River Were Not Simple Options
With a structure weighing thousands of tons trapped beneath the Yangtze River, engineers analyzed different possibilities to continue the project. One option was to abandon part of the section and modify the construction plan; another involved drilling a vertical shaft from the surface to directly access the damaged machine.
These alternatives presented enormous technical, financial, and operational challenges. The point of failure was directly under a critical shipping route on the Yangtze, meaning that an intervention from the surface could disrupt river traffic and significantly increase operational risks.
It was then that a much bolder proposal arose: to start excavating from the opposite side of the tunnel with a second tunnel boring machine and have it advance directly to the stalled machine. Instead of attempting to immediately retrieve the stuck equipment, engineers would make the excavation itself the path to reach it.
China Sends Another Tunnel Boring Machine from the Opposite Side
The solution underwent several technical evaluations before being implemented. The second machine began to advance from the opposite end of the tunnel, while positioning systems, sensors, cameras, and measuring equipment continuously monitored its direction.
The challenge was not simply getting to the same underground area. Two machines, each about 16 meters in diameter and weighing 5,000 tons, needed to meet face-to-face with enough precision to later allow for the structural joining of both sides of the tunnel.
With about 100 meters to go, trajectory adjustments became even more stringent. In the last 10 meters, the speed dropped to approximately 1 centimeter per minute, as teams repeatedly checked the position, pitch, and direction of the advancing machine.
Every small correction was crucial because a few centimeters of difference could complicate the subsequent phase. The meeting needed to occur exactly in the planned area, without any misalignment that could jeopardize the structure or make the connection between the two sides more difficult.
Giants Meet with Just 2 Millimeters of Difference
The contact between the two tunnel boring machines occurred at 11:07 PM on June 22, 2024. After more than a year with the first machine immobilized beneath the river, the second finally reached the point where the equipment had been stuck.
Measurements showed an exceptional result: no horizontal deviation and only a 2-millimeter vertical difference. The project was working with a tolerance of approximately 100 millimeters, meaning that the final vertical error represented only about 2% of the expected margin.
The precision achieved allowed the project to advance, but the mere contact between the machines did not solve the problem. The two machines remained isolated by steel structures and surrounded by saturated sand, with the pressure from the Yangtze River acting on the entire region.
Before opening the meeting area or dismantling any component, engineers needed to create a barrier capable of preventing water from entering. The next step turned the surroundings of the tunnel boring machines into a sort of frozen block of soil.
Engineers Freeze the Ground Beneath the Yangtze
Workers performed 363 high-precision drillings through the metal structures to install pipes used in the ground stabilization and freezing process. The drillings passed through steel parts with approximately 80 millimeters of thickness, requiring strict directional control.
Before executing the final operation, teams even built a full-scale 1:1 reproduction of part of the structure. Workers trained the procedure for about 45 days, while the actual drilling phase took more than five months to complete.
After that, the soil around the meeting zone was frozen to form a barrier about 3.9 meters thick. The average temperature of the frozen area was maintained at around -13 °C, creating a temporary protection against water and sediment.
This layer acted as a safety subwall. Only after stabilizing the area could engineers begin to remove parts of the machines and open enough space to turn the two separate sections into a single tunnel.
Freezing Could Also Displace 5,000-Ton Machines
The freezing process itself posed another problem. When water in the soil freezes, it expands, and this movement could exert additional forces on the thousands of tons of machinery and the already installed concrete structures.
Technical data released later indicated maximum displacements of approximately 13.3 mm and 14.81 mm for the two tunnel boring machines during this phase. These values were well below the reference of 100 mm considered during the operational planning.
Controlling these movements was essential to preserve the precision achieved in aligning the machines. After managing to align giant equipment with only a 2 millimeter difference, engineers still needed to prevent the freezing from significantly altering their position.
Only once the ground was stabilized was it possible to start one of the most labor-intensive phases of the entire operation: cutting and removing the tunnel boring machines themselves without compromising the frozen barrier that kept the Yangtze River out.
Tunnel Boring Machines Had to Be Cut Under the River
Although the operation is often described as a rescue, the tunnel boring machine valued at approximately US$ 50 million was not removed intact from the subsurface. The size of the machines and the lack of space for lifting forced teams to disassemble them within the tunnel itself.
The work involved approximately 2 thousand tons of cuts, transforming parts of the structures into more than 2 thousand pieces small enough to be transported through the tunnel. Among the components removed was the main drive unit, which alone weighed about 320 tons.
This stage generated a lot of heat due to cutting and welding operations. At the same time, just a few meters ahead, the freezing system needed to keep the soil below zero to prevent the barrier around the machines from losing its capacity to contain water and sand.
Teams had to continually balance these two opposing conditions. The disassembly process extended for about 120 days, while the cooling system continued to operate to ensure the safety of the meeting area.
Tunnel Under the Yangtze Will Be About 6.4 Kilometers
The main Jiangyin-Jingjiang Tunnel is approximately 6.445 kilometers long and is part of a larger project measuring around 11.8 kilometers. The structure is designed with six traffic lanes, three in each direction, and a maximum speed limit of 80 km/h.
The initial investment for the project was estimated at around 14.36 billion yuan. In addition to improving road connectivity in the Jiangsu region, the project has become a benchmark for future tunnels constructed in areas of great depth and high water pressure.
The experience has also shown that under specific conditions, two tunnel boring machines can work from opposite ends and meet underground with millimeter precision. This strategy can be especially relevant in very long tunnels, where excavating from only one direction would significantly increase construction time.
In the case of the Yangtze, however, the solution emerged from an emergency. The underground meeting method was not only a way to expedite the construction but also the alternative found to reach a 5,000-ton machine that had become almost buried under the river.
Project Expected to Open in September 2026
After the machines met in June 2024, additional months were required for freezing, disassembly, connection, and structural finishing. The initial opening of the junction area occurred in 2025, while subsequent stages allowed for the definitive consolidation of the link between the two sides.
The main structures of the project have already been completed, but final work includes electromechanical systems, road safety equipment, signaling, and other necessary facilities for operation. The latest official estimate suggests that the tunnel could be opened to traffic in September 2026.
The episode that began with a tunnel boring machine costing approximately US$ 50 million, immobilized 54 meters under the Yangtze, ultimately resulted in an unusual engineering operation. Instead of attempting to pull the machine back, China sent another tunnel boring machine from the opposite side, advanced more than 1.7 kilometers, and positioned two giants with a 16-meter diameter face-to-face with only 2 millimeters of vertical difference.
After that, it was still necessary to freeze the soil, drill hundreds of points in the structure, and dismantle thousands of tons of steel under the river. A failure that could have compromised one of the largest underground projects in the region ended up becoming one of the most impressive engineering feats recorded in the project.
