Civil Engineering Reference
In-Depth Information
Figure 2.8
The Maastunnel under construction in 1941. (Photo courtesy of A. Scheel.)
The rectangular concrete section became the standard construction tech-
nique for these many European road and rail tunnels. The Dutch and the
Danish contractors and designers involved developed considerable exper-
tise and experience, which they subsequently managed to export around
the world. Concrete immersed tunnels were also built in Germany and
Sweden. Christiani & Nielsen also built two concrete tunnels in Canada
in the 1960s with Per Hall as the designer. At this time, the Japanese also
showed interest in the technique. Their first immersed tunnel, at Haneda,
adopted a different approach with a prestressed concrete design, albeit with
a steel outer layer, and was opened in 1964.
The technique spread around the world, and in general, the reinforced
concrete section became the preferred option. The United States favored
their steel shells, Europe universally adopted reinforced concrete, while the
Japanese developed both. The most concentrated development of immersed
tunnels is across Hong Kong Harbor, where five immersed tunnel crossings
have been built (two road, two rail, and one road/rail combined), and at
least two more are proposed. The shallow depth of immersed tunnels is
particularly appropriate to somewhere like Hong Kong, where urban devel-
opment presses in along the sides of the harbor and the approaches to the
tunnel have to be as short as possible. In addition, the underlying granite
could make it very difficult to bore a tunnel.
As more tunnels were built, the construction methods were refined. For
example, initially, the sand foundation material under the tunnel was jetted
in place using external plant. A rig was supported on the top of the tunnel
and moved along the length of the tunnel. A sand-water mixture was piped
down the outside of the tunnel and injected in underneath the tunnel. The use
of such plant in the waterway was an obstruction to navigation that would be
better avoided. The Dutch developed a method of placing the foundation by
