Working in cold weather and tight quarters, workers removed concrete in preparation for repairs to the guide wall at Lock and Dam Number Six. A $1.3-million project will replace a system used to keep barges from being sucked into the dam.
by CHRIS ROGERS
It is an engineering marvel that has reshaped one of the world’s largest rivers and allows 15 million tons of cargo and thousands of small craft to travel every year. But even the mightiest structures have to be repaired sometime. So, crews are working through the winter to shore up Lock and Dam Number Six and other Upper Mississippi River locks.
After working her way up from a job as a clerk in the 1980s, Rojean Heyer has been the lockmaster at Lock and Dam Number Six for nine years. She points out the spot where the suction of water pouring over the dam starts pulling at barges passing through the lock. The only thing that prevents the barges from being swept away is a sliding cleat called a kevel and a tow rail anchored into the concrete guide wall.
Dams on the Mississippi River are dangerous. Like black holes, they pull everything toward them and often claim the lives on anyone unlucky enough to go over the edge.
When a northbound tow — a set of barges is called a tow — locks through at Lock and Dam Number Six, its crew has to break the tow into two pieces because the lock chamber is not long enough to fit a full 15-barge tow at once. The aft-most six barges and the towboat wait downstream, the foremost nine barges are sent through the lock. Once the lock chamber is fully flooded and the upstream gate opens, the first nine barges are tied onto the kevel and pulled out of the lock using a winch system. The kevel keeps the barges tight against the guide wall while the towboat and remaining barges lock through. The kevel is crucial, Heyer explained, because the current wants to pull barges away from the guide wall and over the dam, especially when the river is high.
“I’ve been around for a few accidents, but nobody was hurt,” Heyer said. “It’s more dangerous with high water,” she added. Lately, there has been high water on the river more frequently than in the past, Heyer said. Right now, for instance, the flow was at 70,000 cubic feet per second, compared to a wintertime normal level of 30,000 cubic feet per second, she reported.
It is that kevel, rail, and concrete guide wall that contractors are currently working to repair and replace. “We want to make sure it’s strong enough so that when we have high flows, the barges don’t get loose and have an incident,” U.S. Army Corps of Engineers (USACE) Contracting Officer’s Representative Scott Baker said. “The concrete was older. The epoxy that was holding the anchors in — we had concerns about that, so we wanted to start over with new anchors,” Baker explained.
Last week, workers chipped away at the top four inches of guide wall in preparation for pouring fresh concrete. They will set new anchors for a new rail, weld sections of rail into one continuous piece, and install a stronger kevel to travel along the rail.
That sounds simple enough, right? Working on the narrow guide wall in the middle of winter poses some unique challenges, said Baker and Arne Thomsen, the site safety and quality-control manager for Kraemer North America, the construction contractor.
Because there was a concern that larger equipment would damage the lower portions of the guide wall and because the top of the wall is only a few feet wide, workers had to use small, hand-held jackhammers to chisel away the top layer of concrete, Thomsen said. His company searched far and wide to find a mini-excavator — a sort of itsy-bitsy backhoe only around three feet wide — that would be small enough to work on the wall. Some days, the company can use barges as a floating work surface, but conditions change quickly on the river. Last Wednesday, corps staff said the river was clear and open, but by Thursday morning it was jammed with ice floes that would have made bringing in a barge impossible. “It’s not an easy site to get to,” Thomsen said.
The cold weather can make concrete work and welding difficult, too. The crews use electrical blankets to heat up the wall to allow for pouring concrete. “We lay those down to try to pre-heat the surface,” Thomsen explained. Once the concrete is poured, the workers tuck it in with more blankets on top to keep it warm enough to set properly.
The $1.3-million repair job on Lock and Dam Number Six will wrap up in March, just in time for another season of shipping. Other local locks are also slated for repairs this winter and next.
Heyer was glad to see the new system going in. “It needed to be done,” she stated.