China's 'deep-sea space station' debuts after 3-year R&D

During construction of the Jintang subsea tunnel on the Ningbo-Zhoushan Railway, China deployed its self-developed saturation pressurized tunnel boring machine (TBM) system, known as the "deep-sea space station."

On February 6, the system completed its first 75-meter-deep high-pressure TBM intervention on the Ningbo side. It operated continuously for 22 days and replaced 46 cutters, surpassing the traditional 60-meter safe depth limit for pressurized intervention.

The Jintang subsea tunnel is 16.18 kilometers long, including an 11.21 km subsea TBM section. Construction involves 24 transitions between soft and hard strata, with problematic ground accounting for nearly 70 percent.

Maximum rock strength reaches 191 MPa, more than six times that of ordinary concrete. Maximum burial depth is 78 meters, with peak water-soil pressure of 8.5 bar. The Yongzhou TBM is equipped with 308 cutters, including 30 percent more rock-breaking disc cutters than standard configurations. More than 2,900 cutters have been replaced so far.

Conventional compressed-air TBM intervention is typically limited to depths under 60 meters. Under high pressure, effective working time is about 40 minutes per day, while decompression requires more than four hours. Workers also face increased risks of nitrogen narcosis, oxygen toxicity and decompression sickness, making frequent deep-sea cutter replacement impractical.

Developed over three years, the system integrates saturation diving technology with TBM construction. Workers reach gas saturation after a single compression and can remain and work continuously at the same depth, with fixed decompression time. The system includes living, transfer and control modules, allowing personnel to stay long-term under seabed-equivalent pressure and travel to the TBM face for maintenance and cutter replacement.

Core subsystems, including pressure control, gas management and emergency support, are domestically produced. Maximum saturation operation depth can reach 100 meters. The Yongzhou TBM has advanced more than 3,000 meters, completing over 60 percent of tunneling work, with seabed breakthrough expected within the year.