QINGDAO, CHINA – Three massive tunnel boring machines, affectionately known as "The Three Dragons," are currently working deep beneath Jiaozhou Bay to create one of the world's longest road tunnels under the seabed. This ambitious project will finally unite Qingdao's economically dynamic west with its historic eastern districts.

Qingdao, home to 10 million residents, has long been split by the 32-kilometer-long Jiaozhou Bay. The western Huangdao district houses major economic zones established in 1985, while the historic city center lies to the northeast. Current connections – a car-only tunnel, ferry, and bridge – cannot handle the growing traffic demand, which increases 15% annually.

• Among the world's largest tunnel boring machines
• Drive power: 6,300 kW and 5,600 kW
• Features accessible cutting wheels for safer maintenance
• Tunneling lengths: 3,258m and 3,255m 

One Service Tunnel Machine (8.14m diameter) 

• Drive power: 2,240 kW
• Tunneling length: 3,253m
• Creates maintenance access between main tunnels
• Pioneered geological exploration for the larger machines 

Extreme Conditions Underground 

The project faces extraordinary challenges: 

• Geological Complexity: Mixed conditions from soft tuff to hard granite (up to 175 MPa compressive strength)
• High Pressure: Up to 10 bar deep beneath the seabed
• Cangkou Fault: 200-meter geological transition zone in the bay's center
• Precision Engineering: Minimum 11.6 meters and maximum of 77 meters of rock cover above tunnels

Developed by Herrenknecht over 30 years ago, this system allows workers to enter cutting wheel chambers under normal atmospheric pressure for maintenance—a significant safety and efficiency improvement used successfully in 46 projects worldwide.

All three machines install heavy precast concrete road elements during tunneling, dramatically reducing project timeline. This technology was specially adapted for the smaller 8.14m machine – an industry first. 

International Recognition 

The Qingdao 2nd Sea Crossing Tunnel was honored as one of the 50 ITA Iconic Projects at the World Tunnel Congress 2024 in Shenzhen, recognizing its significance to the global tunneling industry.

국제적 인정
청도 2차 해상 교차 터널은 2024년 선전 세계 터널 컨퍼런스에서 'ITA 아이콘 프로젝트 50'에 선정되어 글로벌 터널 산업에 미치는 중요성을 인정받았습니다.

With tunneling operations launched in July 2023, the project employs over 200 specialists working around the clock. Upon completion, this engineering marvel will transform Qingdao into a true "Bay Area City" – a connected metropolis no longer divided by water.

The three dragons continue their steady progress beneath the waves, promising to bring prosperity and seamless connectivity to millions of residents in this major Chinese port city.

If you want to learn more about this project, click on the link here and dive into the underwater construction of Jiaozhou Bay.