China has achieved an international lead in comprehensive integrated innovation in constructing undersea metro shield tunnel after the success of cross-ocean Xiamen Metro Line 2, according to Qian Qihu, an academician at the Chinese academy of engineering and a specialist of Chinese protective engineering.

Innovative achievements, such as the application of the engineering technology of the undersea metro shield tunnel in a complex maritime geographic environment, have achieved a breakthrough and are being promoted in some other project constructions.

China is now becoming a world power with advanced shield technology, said Qian at the comprehensive technological evaluation session of undersea metro shield tunnel.

Xiamen metro line 2, the first cross-sea shield tunnel in China, is 2,784 meters long, in which two shield machines with a diameter of 7.043 meters were used. This is the longest and most difficult metro project, according to Wang Xiaoqiong, project head of China railway 14 Bureau Group shield engineering co., ltd.

The undersea geographic structure in Xiamen is complicated, which is full of soft clay, hard rocks, and fracture zone, which causes great difficulties to engineers, Wang added. The whole project has lasted for over four years since 2015.