A massive engineering project is in full swing at a depth of 76 meters beneath Qingdao's sea. The Haitian tunnel boring machine (TBM) on the TJ-05 section of the southern mainline of the Jiaozhou Bay Second Tunnel project completed 953 rings of excavation, surpassing 2,000 meters in progress.

The Jiaozhou Bay Second Tunnel is slated to stretch 17.48 kilometers with a 9.95-kilometer sub-sea section. On the Qingdao side, the tunnel is being excavated using the shield tunneling method for a total distance of 3,255 meters. The project consists of two mainline tunnels and a central service tunnel, designed for a speed of 80 km/h. Serving both passenger and medium-sized freight vehicles, it is expected to be the world's longest and most technically challenging sub-sea road tunnel.

The tunnel excavation has seen significant breakthroughs in shield tunneling technology. With innovative techniques, the China Railway 14th Bureau Group construction team has set a record by advancing more than 140 meters per month through hard rock beneath the sea. The team had also pioneered a new shield machine design for the 7-meter-diameter service tunnel, achieving the world's first synchronous box culvert assembly feat.