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Bridge work
Kathryn Crosby Bridge is being replaced
Journal photo by David Rolfe
Leo Ramirez, the “hole man,” is lowered into a shaft for a piling of the new bridge. The hole man’s job is to set a small charge to break up the rock below.
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Published: February 9, 2009
Updated:
Slender white columns have begun their march across the Yadkin River at Bermuda Run.
Arranged in groups of three, known as "bents," the 48-inch diameter columns will support a replacement for the aging Kathryn Crosby Bridge, which was opened in 1940. Work on the new $15 million bridge began in the spring of 2008, said Darin Waller, an engineer with the N.C. Department of Transportation.
The Crosby bridge has "outlived its useful life," said Pat Ivey, the Division 9 engineer. "We typically design these things to last about 50 years, and it's well over 50 years old."
The new bridge, scheduled to open by year's end, will carry two lanes of traffic in each direction, with a sidewalk on the upstream side for pedestrians. It is being built alongside the existing bridge, which stands on solid pylons rather than individual columns.
The columns for the new bridge are being sunk to depths ranging from 15 to 45 feet, penetrating the bedrock for a solid footing. Like the home handyman's cordless drill, the McKinney Drilling Company's LDH-80 drill rig uses an assortment of drill bits to dig the column shafts.
"We start the hole with a rock auger," said Dale Simpson, McKinney's site superintendent.
Studded with carbide tips resembling the teeth of a Tyrannosaurus Rex, the spiral rock auger chews through the first few feet of dirt and loose rock.
Debris is scooped from the shaft with a "mud bucket," a steel barrel with a bottom that slides open to admit the mud and loose rock.
Continuing through solid bedrock calls for the "shot barrel," a smooth steel drum with a couple of modest notches cut into the leading edge. Tiny steel beads resembling birdshot are tossed into the hole, where they collect in the notches and grind through the tough bedrock.
A "hole man," lowered into the shaft at the end of a cable, sets a small charge to facture the rock core, then lifts out the rubble.
The last of the bridge's 24 columns will rise from the riverbed in April. Steel beams will be flown in to span the bents, creating a new way to cross the Yadkin without getting wet feet.
"Things will move quickly after that," project manager Eddie Morgan said.
■ David Rolfe can be reached at 727-7249 or at drolfe@wsjournal.com.
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