Summary：On the morning of Nov. 6, China's deepest undersea tunnel, part of the Qingdao Subway Line 1, was broken th...

On the morning of Nov. 6, China's deepest undersea tunnel, part of the Qingdao Subway Line 1, was broken through in Qingdao, in east China's Shandong province.

The tunnel is in a "V" shape with the deepest point about 88 meters below sea level. Each square centimeter of the tunnel bears a hydraulic pressure of at least 8.8 kilograms, which means the tunnel must take the weight of 300 cars every time it’s extended by one meter.

The 8.1-kilometer tunnel is also the longest undersea subway tunnel in China.