The Shandong province completed the construction of the longest undersea subway tunnel in China in the coastal city Qingdao.
The 5.4-km-long tunnel connects two stations of and is part of the Subway Line No 8 project in Qingdao.
The eastern side of the tunnel was dug by the slurry shield method, while the western side by the mining method, said Wang Zili, chief engineer of the project.
Multiple measures, including the utilization of a robotic arm, were adopted to avoid water and mud bursts, he said.
The tunnel has surpassed the cross-sea tunnel of the Qingdao's Subway Line No. 1, which has 3.49 km of the line undersea.