Civil Engineering Reference
In-Depth Information
Glossary
This glossary has been developed by the International Tunnelling Association,
Working Group 11—Immersed and Submerged Floating Tunnels, and is
reproduced here with their kind permission. It was produced to facilitate
international communication on the subject of immersed tunnels in the
English language. The terms defined relate to typical design and construc-
tion practice for steel and concrete immersed tunnels.
Access shaft
Temporary access shafts are commonly provided to allow
entry of personnel and occasionally equipment to the interior of an
immersed tunnel while floating or submerged. The shafts are usually
removed when alternate access is available, such as along the tunnel.
The access shaft may be attached to the temporary end bulkhead or
may be attached over a temporary hole in the structure, which have to
be made watertight later.
Backill
Material placed around the sides and over the top of the tunnel
within the excavated trench after the tunnel is installed in the trench.
The material is usually granular, rocky, or excavated.
Ballast
Permanent ballast
Nonstructural solid material placed inside or out-
side an immersed tunnel to increase its effective weight perma-
nently. Material placed outside should either be attached to the
tunnel or retained, thereby preventing accidental falling off or
loss of the material. Backfill that may be scoured or accidentally
dredged away is not ballast.
Temporary ballast
Material used to temporarily increase the effective
weight of the tunnel or a tunnel element during the fabrication and
installation phases until replaced by backfill or permanent ballast.
The material may be solid or liquid.
Ballast tank
Temporary tanks constructed within a tunnel element for
the purpose of filling with temporary water ballast to increase the
weight of the tunnel to aid trimming of the element while floating, to
