Mississippi River Bridge in Vicksburg moved due to low water
Published on Thursday, October 26, 2023 at 3:22 p.m.
The former Highway 80 bridge, colloquially known as the Mississippi River Bridge in Vicksburg, has moved 1.5 inches westward over the past year due to repeated water receding events.
Herman Smith, superintendent of the Warren County Vicksburg Bridge Commission, said changes are not new for a structure of this size, but noted that a change of 1.5 inches per year is significant. This change is caused by a drop in river water level and mainly affects piers 2 and 3 of the bridge.
“It’s been changing ever since it was built. It moves when the water goes down,” Smith said. “The fault line runs very close to the bridge and is impacting the Interstate 20 bridge as much as our bridge. That’s kind of how we discovered it. is.”
When the bridge was built, the designers didn’t know that the New Madrid Fault Line runs through Vicksburg along the Mississippi River. Smith said the fault runs south of Interstate 20, through the Ameristar Casino parking lot and onto North Frontage Road.
“When the water no longer saturates the sand, the two plates shift,” he says. “Once the water compaction is gone, the soil begins to move.”
Last year, Smith said his office received a call from the Louisiana Department of Transportation and Development (LDOTD), which manages the I-20 bridge in Vicksburg. The department reported movement of bridge piers and asked Smith if he had seen similar movement on the Old Mississippi River Bridge.
LDOTD spokeswoman Erin Buchanan said Thursday that the changes to the bridge are not alarming. In fact, she said there was work earlier this year to address some changing concerns.
“Typically, bridges like this are designed to be flexible to events such as wind and temperature changes, and to be able to adequately withstand the weight of loads passing across the structure,” Buchanan said. . “In April 2023, DOTD made a knuckle adjustment to allow the bridge to move more. Natural movement of the structure would require repairs to various components of the bridge, so I We monitor those needs on a regular basis.
“Finger joints are an integral part of bridges, not only providing support as vehicles pass over them, but also preventing water and other substances from impacting the steel support girders and bearings.”
Smith said similar plans are in the works for the Old Mississippi River Bridge. Engineer Rudy McClellan, who has worked on the bridge for more than 30 years and now works for Hval and Associates in Baton Rouge, has already designed a plan to deal with the pier movement.
The project will be put out to tender soon. Although the restoration project will result in some closures for railroad operators, there is no risk to using the bridge at this time, Smith said.
“Pier 2 is nothing new to us, but it has continued to change since it was built. It has moved more than 30 inches to the west since it was built,” Smith said. “There is no need to worry (about the safety of the structure) because some repairs have already been made to the movement last year.”
“No one has to worry because we’re monitoring it. We take frequent measurements and the computer can pick it up and predict where it’s going to go,” he added. . “The Vicksburg Bridge Commission is fortunate to have workers who monitor the bridge every day.”
Buchanan had similar comments about the Interstate 20 bridge, one of the busiest thoroughfares in the United States.
“These are naturally occurring events and motorists should keep in mind that the bridge is safe to drive on as we continually monitor the structure for any maintenance needs.” Buchanan said.
The Mississippi River’s water level remained low at -0.17 feet as of 3 p.m. Thursday, but is expected to rise above it on Friday for the first time in more than a week.