Operators in China control a 442-foot (135-meter) tunnel-boring machine from a ground control center about two miles from its excavation point under the sea, monitoring its progress using cameras, sensors and real-time alerts.
The machine, named Yongzhou, is excavating part of the Jintang undersea tunnel that connects Ningbo and Zhoushan in Zhejiang province.
From the Ningbo side, it has advanced more than 13,123.3 feet (4,000 meters), completing about 83 percent of the planned excavations.
As it approaches a section about 305 feet (93 meters) below the ocean floor, the machine faces increasingly difficult bottom conditions. Remote controls allow operators to control excavation from the surface while personnel remain on board and monitor operations.
Control from the surface
The remote control platform connects the ground control center with the machine’s underground operating systems. Cameras and sensors monitor drill head condition, cutter wear and excavation parameters, helping engineers identify problems as they arise.
The monitoring system also sends alerts directly to engineers’ smartphones, covering issues such as abnormal wellhead torque, tunnel segment movements, and changes in oil and seal pressure.
“The intelligent system of this tunnel boring machine (TBM) is more sensitive than humans,” said Dong Bing, senior mechanical engineer of the Yongzhou Railway Project.
The team is also working on greater automation. Deputy TBM operator Cheng Jie said future operators could initiate propulsion with a start command, with the machine then following preset parameters. This ability remains a development goal.
Cutting through difficult seabed rocks
Built to handle the project’s challenging geology, Yongzhou has an excavation diameter of 47.8 feet (14.57 meters) and features 308 cutters. It became operational in May 2024.
Almost 70 percent of the route on the Ningbo side consists of unfavorable ground conditions. This includes hard rock, soft ground and sections where the drill head hits both materials at the same time.
According to the report, the rock strength reaches 240 megapascals, more than eight times that of ordinary concrete.
The conditions caused extensive damage to cutting equipment. Around 4,000 knives have been replaced so far.
Previously, excavation required around one knife change per meter of advance. In more difficult sections, a cutter may need to be replaced after just a few dozen centimeters.
Dong said the machine is expected to reach the deepest section by the end of 2026.
Pressure chambers support cutter repairs
To keep the machine below the seabed, workers must go into a high-pressure environment.
A saturation pressure intervention system allows technicians to live in a hyperbaric chamber and work in shifts for periods of up to 28 days, reducing repetitive compression and decompression.
During the first deployment in February, nine saturation divers worked in three groups over 22 days, replacing 46 cutters at a depth of approximately 75 meters below the seabed.
Yongzhou will eventually meet Dinghai, another drill advancing from Zhoushan. Both machines will then be dismantled in the tunnel.
The Jintang Tunnel extends for 10 miles (16.18 km), including a 6.96 mile (11.21 km) shield drive section. The Yongzhou Railway is expected to open in 2028, enabling a rail connection to Zhoushan and shortening the Ningbo-Zhoushan high-speed line to 26 minutes.
