COASTAL OBSERVER

George Chastain knows what happens when accidents block the Highway 17 bridges leading into Georgetown. He knows what to expect when traffic over the Waccamaw River bridge is reduced to one lane in each direction for three months this winter.
“You know how traffic backs up now,” said Chastain, the executive director of the Baruch Foundation, which owns Hobcaw Barony. “What’s the impact going to be?”
He was among about a dozen people who went to talk with staff from the state Department of Transportation last week to find out.
DOT has a $40.3 million plan to replace four of the bridge supports. Work will start this fall. Lane closures are scheduled to run from Jan. 3 through March 22.
Charlie Ball knows something about lane closures. He is executive director of Friendship Place, which is the beneficiary of the annual Bridge2Bridge Run. The race was moved from the fall to March this year to avoid hurricane season. The 2024 race will be run in April.
Even if the work falls behind schedule, Ball figured the DOT closure plan would leave a path for the runners.
“There’s no good time to close the lanes,” Chastain said.
Late March is a busy time for tours at Hobcaw Barony, and if traffic backs up visitors may decide to go elsewhere.
Still, Chastain said he was encouraged to learn that DOT has met with public safety officials to make sure accidents don’t lead to the complete closure of the highway.
Just over 25,000 daily trips are made on that portion of Highway 17, according to DOT.
This is the first major repair to the bridge since it was built in the early 1960s, said David Hoff, Southeast area principal for Consor Engineers, which designed the project.
“Every five or so years we have to inspect the underwater portion. Over time we found some scour,” he said.
The current in the river had eroded the limestone, mud and silt around the bottom of two of the 14 sets of piers that support the bridge. The problem areas are on either side of the central piers, so to save on the cost of mobilizing the construction equipment for future repairs DOT decided to replace four sets of piers in the middle of the span.
The river is part of the Atlantic Intracoastal Waterway, so the bridge has a 120-foot-wide navigation channel in the middle with a clearance of just over 65 feet at mean high water.
The project will install “crutch bents” at the four piers. That involves creating new columns outside the existing piers and connecting them with girders. The deck structure will be reinforced with steel plates, which is why the lanes will be closed.
“This crutch-bent approach is a little outside the box because of the depth of the water, the height of the superstructure – it’s very, very tall so the engineering had to be such that we needed more foundation members to create the stability necessary to support it,” Hoff said.
The river is over 20 feet deep at the bridge, and Hoff said the new pilings will extend about as far under the riverbed as they will rise above it. The steel casings that make up the foundation of the pilings will be rotated so they drill into the riverbed. Vibration from driving the foundations could alter the soils around the exiting piers, he said.
The girders that will link the columns are 6 feet wide and 8 feet tall. The reinforced deck will be jacked up, the existing bearings removed and the deck will be lowered onto the new girders.
The old piers will be removed down to the water line, Hoff said, so if they shift due to continued scouring there won’t be any impact on the new columns.
The work won’t increase the width of the road or provide room for a bike path, which was once considered for an extension to the Bike the Neck route.
“If we went that direction, it would have to be the entire bridge. You can’t just widen out three spans,” Hoff said. “From our inspection work, the rest of the piers are fine. They’re not having any scour issues.”