These are models of arch-type segments of two possible types of prefabricated tunnels
for the Bering Strait QUADRAIL railway crossing. These are HO, or 1:87 scale, models
that are 12 inches in length, or 87 feet actual length. These models would be about
303 feet in full length (about the length of a football field), or five miles in
The segment depicted on the left in the above photo is a dual QUADRAIL track tunnel
segment and the one on the right is a single QUADRAIL track tunnel segment. The walls
and floor of the segments is approximately 6 feet thick. (Actual thickness to be
determined by structural engineering.) The superstructure framing could be fabricated
with arch-shaped H-beams and H or I-beam horizontal segments imbedded in the flooring.
A type of concrete could be used that presents a barrier to seawater penetration
in order to prevent corrosion of the superstructure framing. A steel liner plate
could be used for the inner walls of the tunnels. This would serve as the inner forms
for pouring the concrete. The outer forms could be made of fiberglass, or some type
of plastic, in the form of removable sections that could be reused for the consecutive
fabrication of identical tunnel sections.
The tunnel sections would be fabricated in a dry area surrounded by man-made dikes
fabricated from excavated rock and crushed stone. The tunnel sections would be temporarily
capped on the ends to make them air and watertight. They would be subjected to about
8 atmospheres of pressure when set in their respective permanent locations in trenches
in the Bering Strait. The current depth in these locations is about 30 fathoms (180
feet) between the Diomede Islands and the coast of Charles Prince of Whales, Alaska
and 27 fathoms (162 feet) between the coast of Russia and the Diomede Islands.
The dual QUADRAIL tunnel sections would experience higher structural loading forces
than the single tunnel sections. However, half of the number of individual tunnels
would be required for the dual QUADRAIL design and more space would be available
for utilities (fiber-optic telecommunication lines, electric power transmission lines,
and possible oil and natural gas pipelines), and allow more area for bypass air induced
by “piston action”, as trains pass through the tunnel. The dug trenches would have
to be deeper for the dual QUADRAIL tunnel sections than for the single tunnel sections.
However, the overall trench width would be a bit wider for the single tunnel sections
for placement reasons.
One possibility for the fabrication site structure is a long temporary steel structure
of sufficient length to allow for the length of the tunnel sections, fabrication
equipment and materials, and width that allows space for the width of all tunnel
sections to be fabricated plus work area. Another possibility is a large inflatable
temporary structure similar in design to temporary aircraft hangers like the ones
used in the military. Tunnel section fabrication in the Bering Strait area has the
advantage of shorter towing distance and time and less exposure to harsh seas during
transport. The major disadvantage is the harsh climate. The temporary fabrication
structures would have to be heated in a region that experiences temperatures as low
as –50 degrees Fahrenheit.
The QUADRAIL tracks shown in the models are for illustration purposes. The track
would not be laid till after the tunnel system was complete, thus reducing overall
weight of the sections. The size, shape, wall thickness, average density of the tunnel
sections and the volume displacement and local seawater density would determine the
buoyancy of the tunnel segments. If the buoyancy is slightly positive, then the tunnel
segments could be floated into position, then temporarily flooded and sunk into their
respective trenches till sea walls and dikes are fabricated and the water pumped
out. If the buoyancy were slightly negative, then pontoon barges with cables and
winches would be required to tow the tunnel segments to their respective trenches.
If it proves impossible to design prefabricated tunnel segments this long then bored
tunnels would have to be considered.