The Dangerous Art of Tearing Down Bridges, Dams, and Aircraft Carriers
History venerates the builders of great bridges,
dams, and towers. But rare are commemorative plaques for the
un-builders—those charged with the equally heroic task of dismantling
those grand structures, once they become dowdy, obsolete, or downright
dangerous. Herewith, five case studies in the art of
mega-destruction—starting with the old, seismically shaky eastern span
of the San Francisco–Oakland Bay Bridge. Also: remodeling NASA’s rocket
assembly building, scrapping the world’s longest aircraft carrier,
recycling a supercomputer, and moving a river to remove a dam.
1. Last Exit for the Bay Bridge
Demolition began: November 2013 | Duration of project: 3 years
Built during the Great Depression, the eastern span
of the San Francisco-Oakland Bay Bridge was a marvel of utilitarian
efficiency. (Some of the construction cranes were even incorporated as
part of the structure.) But now that its graceful replacement is
operational, the old span has to be taken down—without dropping anything
into the water. Expected cost: $240 million. —Eric Smillie
To figure out the best sequence for removing the high-tension pieces, engineers will use a 3-D model, based on structural analysis and historical records, that shows how the forces are distributed. Bryan Christie Design |
Control the Tension
The piers of the cantilever truss
aren’t holding the bridge up. They’re holding it down. “This is like a
highly strung bow,” says senior bridge engineer Brian Maroney. (A bow
made of 50 million pounds of steel.) “You don’t want to just cut the bow
because the thing will fly off in all directions.” So crews will first
remove the pavement on the upper deck to lighten the bridge’s load and
reduce the tension. Next they’ll isolate steel supports, jacking them
out of tension until they can be cut without whipping apart. Then
they’ll slowly release the jacks.
Cut the Truss Spans
Named for their length in feet, the
504 and 288 truss spans are not under as much tension as the cantilever,
so there’s less chance they’ll explode in your face when you cut into
them. Still, caution is called for: The 80-year-old steel is not like
modern steel; crews must be prepared for differences in strength and
hardness.
Cart the Pieces Away
The steel beams are coated with
greenish-gray paint, under which is a coat of lead-based stuff. To avoid
contaminating the bay, all that metal has to be trucked away and
cleaned, after which it will be resold as scrap.
Build a Monument
The massive art-deco column of pier
E1, near Yerba Buena Island, may be preserved as a monument to the
bridge that served the Bay Area for 77 years. The E2 pier will also
likely remain and be converted into an observation platform for the new
span.
Blast Foundations
The foundations of piers E3 to E5
are like honeycomb inside. One idea for demolition: Drill into them,
plant a series of computer-controlled explosives around the internal
walls, set off the charges, and let the concrete collapse into the void.
The NASA Vehicle Assembly Building
at Kennedy Space Center is big. Big enough to house the Saturn V rocket
that propelled men to the moon. Big enough to have its own weather
system (mist can form along the ceiling on humid days). And now it’s
getting an overhaul: The seven fixed platforms of the VAB’s High Bay 3
must be detached, moved outside, and demolished to make way for a
modular system that can better accommodate a variety of different
rockets and exploration programs. Here’s how contractors are completing
one of the world’s largest renovation projects. —Bryan Gardiner
Old Platforms Out
The first step was to remove the
seven huge steel platforms (weighing 140 to 230 tons apiece) that once
hugged shuttles and rockets. Precise centers of gravity had to be
calculated for each of these multistory structures. After wiring and
utility systems were disconnected—including some 700,000 feet of copper
cabling—the platforms were detached and slowly lowered to the floor by a
ceiling-mounted bridge crane. Careful movement was essential to prevent
sway. Good thing this crane is precise enough to touch its load to an
egg without cracking it.
New Platforms In
The old fixed platforms will be
replaced with a modular system of 10 platforms that can be repositioned
vertically and horizontally. That flexibility will be crucial for NASA’s
new Space Launch System, which will rival the Saturn V rocket in size
and is designed to offer a variety of configurations for different
missions. The facility is also expected to host much smaller rockets
from commercial space companies.
3. The End of the Enterprise
Demolition began: 2012 | Duration of project: 14 years
After more than 50 years of service—including a cameo in Top Gun—the 100,000-ton USS Enterprise
was inactivated in late 2012. It will be the first nuclear aircraft
carrier of this class to get dismantled (in fact, “Big E” is the only
ship of its class ever built), and the Navy estimates the project will
take about 14 years. —Bryan Gardiner
1. Ordnance Off-Load
To transfer some of the ship’s munitions, Enterprise crew members fired shot lines over to the USNS Sacagawea
and used them to string messenger lines made of wire rope. Then, while
the ships traveled for hours through the Atlantic, just 30 yards apart,
they slid ammunition packages across the water. Sounds crazy, but this
sort of at-sea transfer has been used for supply replenishment since at
least the late 1800s. The remaining ordnance was airlifted across in 946
helicopter trips.
2. Interior Stripping
On December 1, 2012, the carrier
pulled into Norfolk, Virginia, and its contents were stripped—tools,
furniture, linens, technical manuals, spare parts, cryptographic
equipment. Cranes removed weapon launchers, anchors, antennas, and other
large items.
3. Defueling
In June 2013, tugboats towed the
ship across Hampton Roads harbor to Newport News Shipbuilding, where
her keel had been laid in 1958. (Many of the workers taking her apart
are the offspring of those who built her.) Crews then remove the fuel
from the eight reactors, but exactly how they do it is classified. The
empty compartments, along with their radioactive piping systems, are
eventually sealed shut.
4. Spent Fuel Removal
The spent nuclear fuel is placed in
containers with 14-inch-thick stainless steel walls (each cask weighs
about 350,000 pounds). The containers are then loaded onto trains and
trundled off to the Naval Reactors Facility at the Idaho National
Laboratory for analysis and storage.
5. Towing
Onward! To the Puget Sound Naval Shipyard in Bremerton, Washington, via the scenic route. The Enterprise
won’t fit through the Panama Canal, so a tugboat will pull the hulk
around Cape Horn and up the Pacific Coast. During the four-month trip,
the two vessels will be anywhere from 1,200 to 2,000 feet apart,
depending on the waves: Ideally, when the tug goes up on a wave, the
carrier should too. Constant adjustments to the tow length keep them in
sync.
6. Scrapping and disposal
Each steel-encased reactor will be
moved by barge from Puget Sound to the Hanford nuclear storage site,
where it will be buried in a radioactive package that also includes
other nasties like asbestos, cadmium, arsenic trioxide, cyanacrylate
adhesive, and paints containing cyanide, coal tar epoxy, and chromium
trioxide. And the 60,000 tons of steel in the hull? Chopped up and
recycled, of course.
4. Recycling a Supercomputer
Demolition began: 2013 | Duration of project: 1 month
Supercomputers are typically retired
after about five years, and one of the latest to get its pink slip is
Roadrunner, which was officially shut down on March 31, 2013. Built by
IBM and installed in 2008 at the Los Alamos National Laboratory, this
$121 million daisy chain of 296 server racks and 122,400 processor cores
helped model everything from the decay of the US nuclear weapons
arsenal to how white dwarf stars explode into supernovas. Scrapping the
housings and connections was the easy part; steel, copper, and plastic
components were all shredded. But Roadrunner also contained 34 disk
drives, some of which almost certainly held sensitive information. Los
Alamos doesn’t share the specifics of the removal and destruction
process, but previously published guidelines from the US Department of
Energy and the National Institute of Standards and Technology provide a
sense of how it works. —Bryan Gardiner
Overwrite, then apply magnets … or destroy completely.
First, technicians overwrite data
three times, twice with pseudo-random patterns and once with a known
pattern. Then some disks are demagnetized, while others may be sent to a
separate metal-destruction facility. Some places use a disk sander to
abrade the recording surface. Others feed disks into a crusher, which
pushes a steel piston through the center of the drive. Still others
apply concentrated hydriodic acid solution.
5. Moving a River to Remove a Dam
Demolition began: 2013 | Duration of project: 3 years
California’s San Clemente Dam opened
in 1921, and today its reservoir is choked with silt. That means an
earthquake or flood could send a wall of mud sliming down the Carmel
River and the valley below, damaging more than a thousand buildings. So
dam owner California American Water and state and federal resource
agencies decided to take it down. Dynamite isn’t an option because of
the dirt and water that would spew forth, so engineers decided to move
the river instead. —Eric Smillie
Cut a Notch
Crews are going to cut a
450-foot-long canyon through the ridge behind the dam and carve a new
river channel around the sediment to neighboring San Clemente Creek.
“I’m not aware of any other dam removal project that’s looked at that
type of option,” says Richard Svindland, director of engineering for
California American Water. “River rerouting is tough to do.” This
Herculean task, the largest dam removal in state history, will involve
building a diversion dike to direct the water along its new course.
Demolish the Dam
To make way for the water, workers
will haul 380,000 cubic yards of sediment from San Clemente Creek (where
the new river will run) and dump it on the main heap of silt, which
will remain permanently. Then they’ll pick the dam apart with hoe rams.
Eventually, the rerouted river will flow through the spot where the
structure once stood.
Watch and Wait
In five years, California American
Water will hand the site over to the Bureau of Land Management.
“Ideally, 20 years from now,” Svindland says, “you won’t know that a dam
was ever there.”
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