Two workers work in the under-construction Qianjiang cross-river tunnel in Hangzhou, east China's Zhejiang Province, April 18, 2011.

The under-construction 4.45-kilometer-long tunnel under the Qiantang River is adopted by the outside diameter of 15.43 meters shield technology, six-lane twin-tube, as the world's largest diameter of one of sheild tunnel. (Xinhua/Xu Yu)