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Emergency
Bridge Demolition
By
Brent Blanchard
(Originally
published in The Journal of Explosives Engineering USA
and Demolition & Recycling International)
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As
most veterans of our industry are aware, explosive demolition
by its very nature is often a challenging proposition. Even
under the best circumstances, proper planning and care must
be taken during a variety of processes to ensure a safe, successful
result.
However,
every now and then a project suddenly arises where safety, timing
and cost factors combine to form a critical scenario that requires
rapid execution in an environment far more challenging than
the norm. On these occasions, the stresses, complications -
and most notably dangers - increase exponentially, and conspire
to test the mettle of even the most seasoned experts.
In an unusual convergence, this situation occurred three times
over the past few weeks as several contractors endeavoured to
complete emergency bridge-blasting projects around the world
on very short notice. In each case, normal age, wear, and deterioration
factors had nothing to do with the structure's instability.
In fact there were virtually no common elements linking the
projects. Yet each stands on its own as a noteworthy achievement
and a credit to our industry.
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Interstate
40 Bridge
Weber
Falls, Oklahoma
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People
across the United States celebrating Memorial Day weekend
2002 were shocked and saddened to see news reports of
a horrific accident near Webbers Falls, Oklahoma.
Two
280-foot barges, weighing a combined 800,000 pounds, had
slammed into a four-lane bridge on Interstate-40. The
impact caused a 500-foot section of the 2,000-foot-long
structure to pancake, sending ten vehicles tumbling into
the murky Arkansas River and resulting in fourteen fatalities.
As
officials from the NTSB, FEMA, Coast Guard, Army Corps
of Engineers, Oklahoma Dept. of Transportation (ODOT)
and a phalanx of other agencies converged on the scene,
they found a daunting sight: Fourteen of the span's 50
structural elements were either badly damaged or destroyed
from the impact.
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The
western-most pair of its 26 spans were ripped from
headwall anchors and landed on the ground below.
To the east of this damage, a second pair of spans
partially collapsed and tilted into the riverbed.
A third also suffered damage, coming to rest on
the barges, while a fourth pair was completely submerged
at the bottom of the river. In addition, four 60-inch
thick reinforced concrete pier columns were partially
destroyed and two others pushed dangerously off-center.
Once
all rescue, recovery and vehicle-salvage operations
were complete, efforts were focused towards repairing
the bridge, which carries 20,000 vehicles daily
and is considered a critical transportation artery
for the southern United States.
ODOT
contracted Jensen Construction Company as prime
demolition contractor, and Jensen Operations Manager
Gene Spitza immediately asked explosive demolition
specialists at Demtech, Inc. to report to the site
as quickly as possible. Demtech mobilized equipment
and personnel from their Missouri office and the
company's headquarters in Dubois, Wyoming to the
scene within 12 hours, and formulated a plan to
safely demolish the four western-most spans and
piers by the end of the day.
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team then worked from man-lifts and crane baskets
throughout the morning and early afternoon, under
the direction of Spitza and Demtech President Scott
Gustafson, drilling 16 holes in the heavily-reinforced
pier stems and pre-burning 16 cavities in the bridge's
¾-inch thick steel webs just below the flanges
to prepare the site for explosives. Blaster Steve
Rainwater then oversaw the loading of 24 pounds of
Dyno AP emulsion in the pier columns and the attachment
of 23 pounds of 600 to 4,000-grain RDX linear charges
to the flanges and webs of all four spans. |
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True to their word and to the appreciation of Federal
officials, Jensen and Demtech initiated an abbreviated
countdown just before dusk, then pressed the button.
The
blast successfully felled all six structures, and
the following day Demtech demolished both stems
at Pier #2 down to the top of the footing, 38 feet
below the waterline. The entire blasting operation
had taken less than 48 hours, and the final two
eastern-most spans were removed conventionally shortly
thereafter.
Work
on a $15 million replacement section of Interstate-40
is currently proceeding on a similarly accelerated
schedule, and the roadway is tentatively scheduled
to reopen August 8, 2002.
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