ABSTRACT
At the beginning of the 20th century the only known ways to construct a tunnel under a waterway were by simple digging, sometimes under air pressure and by a new “high tech” method, just emerging initially referred to as “Sunken Tube Tunnel”. During the 20th century over 150 tunnels were constructed by this Immersed Tunneling(IT) method. These tunnels were used for many purposes including rail and highway transport, material transport, and the subaqueous crossing for various utilities such as water, sewer, petroleum etc. The Immersed Tunnels are prefabricated in sections 100-200 m. long, sealed by bulkheads at the ends, floated to the tunnel site and lowered into a trench whereby they are joined hydraulically and later backfilled.
