An immersed tunnel in Amsterdam
For the construction of Amsterdam Metro Wayss & Freytag prepared a caisson solution as their special proposal, for which the contract was awarded in 1970. The design was based on the experience the company had gained previously in Berlin with compressed-air foundation works for the metro construction lots H 102 and G 19. The first section, from the central railway station under Weeserplein up to Waterlooplein, was built between 1970 and 1976. The opening ceremony took place on October 16, 1977.
Earth-models served as formwork for the working chambers. This method had first been successfully tested by W&F in 1953 during the construction of the pumping station Duisburg-Stockum – Alte Emscher. By arrangement of intermediate cutting edges according to a W&F patent of 1933, it was possible to increase the stability and achieve a high precision in a lateral position during the sinking process. W&F first used such intermediate or bearing cutting edges in 1935 during the construction of the sea lock in Ostende. To remove the ground during the sinking process, fixed mounted jet mud guns were used. This epoch-making method was also developed by Wayss & Freytag and first introduced in 1932 during the extension of the Eastern mole in Dunkirk.
After they were sunk, the 40 m long caissons were connected to each other by watertight expansion joints. Special attention had to be paid to the concrete mixture, since the structure was not only exposed to high compressive stresses, but also had to be watertight and, during the construction phase, it was also exposed to high thermal stresses. To keep down the concrete temperatures, pipes placed inside the caisson were used for cooling.