New and Future Bridges - Pushing the Limits: New Adventures in Engineering - page 81

world-class bridge-designing firm of T. Y. Lin International to study the feasibility of constructing a
bridge or bridges across the strait. Because of the extreme depths of the water and the high volume
of shipping at the location, a clear objective was to have as few piers as practicable, which obvi-
ously meant having the longest possible bridge spans. This led T. Y. Lin himself to propose a bridge
across the nine-mile route that would have only three piers but in water as deep as 1,500 feet and
with spans as large as sixteen thousand feet. Although this is well beyond the length of the main
span of the Akashi Kaikyo Bridge, the generally agreed-on feasibility of the proposal supported the
hybrid design put forth by Lin.
Proposed bridge across Strait of Gibraltar
The design combines features of suspension and cantilever bridges, with the suspended span be-
ing about ten thousand feet long and the cantilever arms reaching out about 3,300 feet each. The
design is reminiscent of the 1920s proposal for an ungainly cantilever-suspension bridge that non-
etheless enabled Joseph Strauss to promote the creation of a Golden Gate Bridge and Highway Dis-
trict, a crucial step in getting that bridge built. The original ungainly design for the California struc-
ture evolved into what many consider still to be the most beautiful bridge in the world. Lin also
proposed as an alternative design for Gibraltar a combination suspension and cable-stayed bridge
but recognized, as Strauss eventually did, that “the aesthetics of this system can stand some im-
provement.” The fundamental thing in the conceptual design stage is to establish feasibility within,
or even reasonably and defensibly beyond, the state of the art.
As an alternative to a bridge, a tunnel beneath the Strait of Gibraltar was proposed as early as
1869, the year the Suez Canal was completed. Large projects have always emboldened engineers to
propose still larger projects, and in recent years the completion of the Channel Tunnel has renewed
interest in a tunnel scheme between Spain and Morocco. Exploratory borings have been made in
Morocco, to depths of one thousand feet. The clay found there is common to the two coastlines,
but what lies in a tunnel's path under the strait cannot be known with absolute certainty until the
actual tunnel is bored. Likewise, even though the technology of offshore oil platforms may be ad-
opted to set bridge piers in unprecedented depths of water, what surprises might be in store at those
depths will remain unknown until construction actually begins. Such uncertainties, not to mention
the multibillion-dollar cost estimates, are likely to escalate as the realities of a unique construction
project reveal themselves, as they did with the Channel Tunnel, thus keeping a fixed crossing of the
Strait of Gibraltar on the drawing board.