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Sauk
City Rail Bridge
Sauk City, Wisconsin
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Experts
have long agreed that the best way to keep a bridge "healthy"
is to perform routine maintenance. However, on rare occasion
the maintenance and repair efforts themselves bring unexpected
results, as was the case in the Madison suburb of Sauk City,
Wisconsin.
On March 11, 2002 work crews were attempting to make repairs
to a 130-foot section of the Sauk City Rail Bridge when
western portions of the span began to shift downstream.
A stabilization effort began shortly thereafter, however
the structure suffered another major shift on April 11,
bringing all work to a halt.
An engineering study determined that the second event also
caused a six-inch shift in one of the supporting concrete
piers. The study concluded that further repairs to the pier
or the bridge span were unfeasible, and that both would
require complete removal and replacement.
Realizing the potential danger of the situation, representatives
from Wisconsin Rail Transit requested assistance from Chicago
Explosive Services (CES), Chicago, Illinois.
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CES
President Patrick Carney arrived on scene shortly
thereafter, and his team set about re-assessing the
span's condition. Carney determined that pre-cutting
steel supports to facilitate placement of explosives
was out of the question, and that powerful 4,000-grain
RDX linear charges would be required to ensure a safe
and complete collapse. The Chicago Explosives team
also recommended pre-cutting the flanges of the rails
themselves to facilitate a perfectly perpendicular
descent into the Wisconsin River.
Carney then turned his efforts to damaged pier #4,
and devised a plan that would allow holes to be drilled
into the pier at several strategic locations without
the risk of further shifting or decomposition. The
holes were then packed with conventional dynamite,
and both structures were prepared and wired within
two days.
An extra-wide, 1,000-foot safety perimeter was then
established around the site, and at the count of "Zero,"
a thunderous blast simultaneously demolished both
the bridge and pier.
When the dust cleared, all that remained were three
large segmented sections of steel awaiting safe retrieval
from the waterway below. Adjacent privately owned
structures that were pre-inspected by Protec showed
no adverse effects from the blast, and ground vibration
levels fell within acceptable levels. |
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