One of the world’s biggest tunnel construction projects now underway is the construction of a tunnel under the Yangtze River in Shanghai, China. The plan is to open the 7.47-km long, three-lane road tunnel under the Yangtze to traffic in time for the World's Fair (Expo 2010) taking place in Shanghai. Two tunnel boring machines (TBMs) from Herrenknecht AG are doing much of the heavy construction work.

Shield excavation tunnel-boring machines such as these are used in complex tunnel projects around the world, and the heart of these massive machines is the main bearing. These multiple-row roller bearings, measuring up to 6 m in diameter and weighing up to 20 tons, hold the rotating cutter and support it against enormous advance forces and massive torque. Special shaft seals, developed by Merkel Freudenberg, Hamburg, Germany, protect the main bearing against the penetration of excavated material, stone, sand, and water. These enormous seals also prevent transmission oil leakage. Manufactured as endless molded rings without joints, seals can measure up to 10 m in diameter and are produced within extremely tight tolerances.

The two TBMs being used in the Shanghai project since the end of 2006 are the largest of their kind, have a diameter of 15.43 m, and each generate a boring torque of 39,945 kNm with an engine output of 2,500 kW. The first TBM is expected to reach its destination shaft on the Yangtze island of Changxing by summer 2008.

Visit Merkel Freudenberg for more information.