Late last night, deep in a Wikipedia hole that started with Transport in Réunion, I wound up in a side tunnel consisting of the world's highest bridges. If you haven't been keeping up, civil engineering's bridge game circa 2015 is completely fucking nuts, and the pinnacle of it is China's Sidu River Bridge.
Image: Road and Bridge Southern China Engineering Co
First of all, at 1,600 feet above the canyon floor below, the almost mile-long bridge looks like it might as well be connecting the peaks of two towering clouds, though in reality it's really just the peaks of two mountains. It's a rather classically designed suspension bridge, calling to mind a sinewy version of the Golden Gate. But it's less the bridge's design that makes it incredible than how it was actually constructed: The first pieces of its suspension cabling, known as pilot cables, were delivered across the chasm of the Sidu River valley attached to a pair of rockets.
The bridge's location is not only highly remote—the closet local road to the site is 3.2 kilometers away, according to a report on the bridge's construction in the journal Civil Engineering—it's also geographically extreme. The valley walls are cut deeply, falling at angles between 75 to 90 degrees, and they're also covered with thick forests. Establishing conventional work sites would require unacceptable levels of environmental damage. Adding to the challenge were the winds that regularly rip through the valley, making helicopter-based work dangerous. Time to call in the army.
Rocket field test. Image: Road and Bridge Southern China Engineering Co
The CE report explains:After evaluating the site conditions and other options, an innovative cable placement method using a military rocket was developed. A special launching system using rockets attached to chinlon rope pilot cables was designed. On October 9, 2006, two rockets were fired to take the two 1,300 m long ropes made of chinlon, a highly elastic yarn, over the canyon, a distance of roughly 1,100 m. The margin for error in any direction was plus or minus 40 m, and the cables landed within 10 to 15 m of their intended locations. To achieve this precision, a trajectory simulation model of the flight of the rocket and cable system had been created that took into account such factors as wind and temperature.
The entire process was completed in a short period—perhaps 10 seconds—and the cost savings were significant. To the best of our knowledge, this was the first time ever that a rocket has been used to launch a bridge suspension cable.
Almost a decade later, the Sidu River Bridge appears to also retain the honor of being the only time a rocket has been used to transport a pilot cable.