Civil Engineering Reference
In-Depth Information
conditions, are also investigated, and the specific aspects that are crucial to
the success of the immersed tube method are explained. The aspects that
benefit from numerical analysis and modeling techniques are noted, along
with guidance for scale model testing—something that is commonly under-
taken for immersed tunnels.
HYDROGRAPHY
Hydrography is the measurement, description, and analysis of natural
waters and their margins. It is essential to understand the hydrography of
the body of water in which a tunnel will be constructed. The aspects that
must be understood and accounted for in the design and construction of a
tunnel are
• Water levels
• Wind and waves
• Water density
• Currents
• Sediment transport
• Ice formation
Each of these aspects is described below. Usually, historical records can
be obtained from weather stations and marine survey stations in the region
where a tunnel project is chosen to be constructed. However, it is unlikely
that comprehensive data will be available for the actual site chosen for the
tunnel and it is normal for the interpolation of existing records to be car-
ried out, to establish initial hydrographic parameters, and for further sur-
veys to be carried out in the years leading up to the tunnel construction, to
get precise data for the project.
Water levels
The variation in water level and, hence, the available water depth, will have
a large influence on the planning of a tunnel. It will dictate construction
methods in terms of floating and maneuvering the tunnel elements. For
example, the tidal range may limit the time periods available for immersion
activities if there is insufficient water depth to maneuver the elements at low
water levels. Water levels will also govern the earthworks that provide flood
protection to the tunnel approaches.
Understanding the maximum and minimum water depth is therefore
important, not only for construction planning, but also to ensure that design
is undertaken to establish the best possible construction techniques for the
given water depth and tidal range. It is usually possible to obtain historical
