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NDDOT Replaces 85-Year-Old Bridge

Mon October 22, 2007 - Midwest Edition
Dorinda Anderson

“When the Liberty Memorial Bridge was first built in 1922 it was the only crossing over the Missouri River from Sioux City, Iowa, to Great Falls, Mont., a 500-mile distance in either direction. The Memorial Bridge was also needed as an arterial route between Bismarck on the east side of the Missouri River and Mandan on the west side of the river, in central North Dakota,” explained Mike Kopp, on-site engineer of the North Dakota Department of Transportation (NDDOT).

“South Dakota had a railroad bridge that vehicles would sometimes cross,” Kopp said. “In the winter travelers could cross anywhere along the river over the ice, but in the spring while the ice was thawing and breaking, the huge ice chunks made it impossible to cross. As many as 10,000 vehicles a year tried one way or another to successfully cross the Missouri River.”

Before the federal highway system was developed there was a trail known as the Red Trail across North Dakota. Travelers moved pretty quickly all the way across the United States but lost time at the Missouri where they had to wait as long as four hours to be ferried across.

About 1912, a rough system of highways was laid out, including the Red Trail that became known as Highway 10, and eventually was replaced by Interstate 94.

Then in 1919 the state of North Dakota and the federal government set out to build a bridge between Bismarck and Mandan. A three-span Warren-Turner through-truss design was developed.

The structure required a year and a half to construct at a cost of about $1.4 million. It was the longest bridge in North Dakota. Upon completion, the bridge was christened the Liberty Memorial Bridge in honor of the North Dakota World War I soldiers, according to the Liberty Memorial Bridge Historic American Engineering Record.

To preserve the historical meaning of that old bridge, the new bridge will include five overlooks, two plazas and two parks, one on each end. The five overlooks will each honor a branch of the U.S. military.

“Talks continue between NDDOT and the Historic Preservation Office on the exact specifications of this project,” Kopp said. “NDDOT’s Cultural Resources Section and the State Historical Society of North Dakota have researched the history of the old bridge, collected old photographs and archived them for use in a Traveling Exhibit.”

“State, federal and local agencies tried to find a way to preserve the bridge but the cost was prohibitive – between $57 million and $69 million to preserve it and an even higher cost to transform it into a pedestrian bridge,” Kopp added. Once construction is complete, demolition of the existing 85-year-old bridge will begin.

The 85-year-old bridge was designed to last only 50 to 70 years and is now in structural disrepair and because it has only two lanes, the increasing traffic flow often bottlenecks. From Feb. 15, 2006, to April 7, 2006, NDDOT temporarily closed the bridge until repairs could be completed to ensure that the bridge was safe for traffic.

The new bridge, with a construction cost of about $47 million but with right-of-way and engineering costs bringing the cost closer to $56 million, will be four lanes wide to handle the expected traffic increase. The current 14,200 vehicles a day is expected to increase to about 17,800 vehicles a day by 2025, Kopp said. The width of the new bridge from outside to outside will be 84.8 ft. (25.9 m) and 2,369 ft. (722 m) long from abutment to abutment.

“Bismarck/Mandan with a combined population of about 115,000, is the largest urban area within 100 miles in either direction, causing it to grow quickly. Also, once the new bridge is complete it is expected that traffic will revert back to the bridge from alternative routes travelers were using to avoid the congestion on the bridge,” Kopp added.

The new bridge is being built south of the existing bridge because that alignment has the fewest right-of-way impacts.

Construction of the new bridge began in June 2006 and continued through the winter, an uncommon feat during the frigid North Dakota winter. Crews took only four days off during the first year of construction due to weather and ice.

“Traditionally, bridges are built working from one end to the other but in this case we are working from both ends and meeting in the middle,” Kopp said, “to avoid ice and high water levels.”

Lunda Construction Co., of Black River Falls, Wis., the prime contractor, started with three large cranes (110, 165 and 210 ton [99.7, 149 and 190 t]). Steel beams for piling were stockpiled on-site and cranes set barge sections in the water to assemble a work platform for a crane and crew. Barges were put in the water so the cranes could be crawled out on the barges from the dock, using two 750-hp (559 kW) tugboats, Kopp said.

Throughout the project several cranes were used, including a small American 5299, a Terex HC 110, a Terex HC 165, two Terex HC 210s and a Globe 650 hydraulic crane. Other equipment included a Samsung 450 excavator track hoe, a Kawasaki Z65 loader, a Cat 28G loader and two 60-ft. Genie man lifts.

Piers are numbered from west to east. Piers 1 and 15 are the abutments. The other piers are freestanding structures. Piers 2 through 6 are on the Mandan side. Piers 7 through 9 are in the river. Piers 10 and 11 are on the sandbar on the Bismarck side. Piers 12 through 15 are on the land on the Bismarck side.

The 165-ton crane was used to build the walls of the project’s first cofferdam for pier 7 on the western edge of the Missouri River channel. The cofferdam is the first step to building the pier foundation for the new Liberty Memorial Bridge. The pier 7 cofferdam was the first of five cofferdams to be built. Pier 8 followed, just to the east of pier 7. Workers vibrated sheet piling 65 ft. (19.8 m) down to build the 35 by 71 ft. (10.6 by 21.6 m) cofferdam. Piling was driven into the ground to support the concrete piers, which in turn support the deck and the traffic loads crossing the bridge. The total project required 37,882 linear ft. (11,546 m) of piling.

Pile driving began in late July 2006, with most of the work being done on the Bismarck side. Once the walls of pier 7 were complete, excavation began inside the cofferdam with the crane swinging clam buckets of mud out of the excavation site so it could be hauled to shore, using the barges, and stockpiled; 45 ft. (13.7 m) of the river bottom was dug out.

In early August 2006 pile driving began on the east abutment and 18 piles, all 80 ft. (24.3 m) long, were pounded into the ground, a process that took about three weeks for piers 2 through 5. Concrete was then poured underwater around the piles in pier 7, requiring approximately 700 cu. yds. (585 cu m) of concrete.

Once the concrete was cured to strength, water was pumped out of the cofferdam, exposed piling was cut to length and the reinforcement steel for the footings was tied. About 7.176 million lbs. (3,254 kg) of structural steel was required for the bridge and the approach, along with just under 20,000 cu. yds. (15,291 cu m) of concrete and about 4 million tons (3.6 million t) of reinforcing steel.

The first piers of the project required more than 200 cu. yds. (153 cu m) of concrete. Lunda Construction placed 45 cu. yds. (34.4 cu m) of concrete in three forms on the east bank at pier 13, and 177 cu. yds. (135 cu m) inside two forms in the cofferdam at pier 7. A total of approximately 19,233 cu. yds. (14,705 cu m) of concrete were required for the bridge.

“The project also required about 300 cubic yards of riprap for each of the 13 footings for the piers,” Kopp said. “Soil for the project is hauled in and stockpiled until it is needed and what isn’t needed is hauled back out. Piers 7 through 11 required the most soil; piers 7 and 8 needed 3,500 cubic yards of soil for the west approach, while pier 9 needed 3,000 cubic yards, leaving about 2,500 cubic yards that had to be hauled out. For piers 10 and 11 about 4,000 cubic yards of soil was hauled in but only about 1,500 cubic yards was used. Three sub contractors were hauling fill throughout the project.”

“There are about 15 subcontractors working on the project, with many working at the same time. During August five subcontractors were working on approach roads, steel erection and rebar. Utility contractors worked to reroute utilities since Liberty Memorial Bridge carries electricity, cable TV and telephone lines between Bismarck and Mandan,” Kopp said.

To prepare for winter temperatures, a large enclosure on the Bismarck side was built so crews could continue working on the retaining wall.

By mid-December 2006 crews were focusing on pile driving for five piers on the west side of the Liberty Memorial Bridge project. Piers 2 through 6 received the majority of attention while the Missouri River water levels remained high and ice floes plugged the channel. As long as mild temperatures continued, crews could start the concrete pours. The concrete was mixed according to NDDOT standards for cold weather concrete pours.

Concrete was poured in the winter and so required extra work to ensure a quality structure. Working with NDDOT, the contractor used two large heaters (750,000 Btu and 400,000 Btu) to keep the forms warm. They were insulated to control the temperatures required for curing the concrete in the cold weather. “The exterior was wrapped with heating tubes and heating blankets while cooling tubes were used on the inside to keep the concrete cool and create a more even cooling temperature, to avoid problems with cracking,” Kopp explained.

In December Lunda had to adjust the work plans when water on the Missouri River rose and froze at its high point. To keep the project moving forward, Lunda work crews moved on shore to finish the east approach and begin pile driving on the west approach for piers 2 and 3.

The Missouri River level dropped about 3 ft. (.9 m) by Jan. 1, 2007, and enough ice had moved out of the area to allow Lunda Construction work crews to resume work on pier 7, the first water-bound pier on the west side. Crews were able to move back out on the water with a crane to set the second pier column form.

Crews continued to work 10-hour days through below-zero temperatures, alternating between piers until all 15 were complete.

Once temperatures warmed up in March, work progressed much more quickly because crews were able to work more efficiently. As the ice in the river thawed, crews worked on both sides of the river as they could, but once it thawed completely crews moved to pier 8 in the middle of the river. Pier 8 required 400-cu. yds. (306 cu m) of concrete, requiring nearly 50 truckloads of concrete to be shuttled back and forth from the Mandan side of the river.

Setting 40 concrete box girders for the east approach followed, causing the Lunda’s crew to be increased from 16 to 25. The first box girder was set on the east approach, between transition pier 12 and pier 13. The girder was manufactured by Cretex Concrete Products of Menoken, N.D., and is 66 ft. (20.1 m) long and weighs 67,000 lbs. (30,390 kg). Some of the longer girders are 96 ft. (29.2 m) long. Crews set up to eight girders each day.

On the opposite end of the spectrum, summer temperatures soared to 100 degrees. “This is kind of intense,” Kopp said of the August temperatures. “During the middle of the afternoon the crews who were working on top of the deck moved below to get in the shade. The cold is worse. Even though it might seem that with the water below the temperatures would be cooler, the cold causes humidity.”

By June 2007, the project was 33 percent complete. Crews are working on the two approach bridges on the east and west sides.

“The substructure is complete and concrete box girders have been set on the east side,” Kopp said. “On the west side the concrete box girders have been installed and crews are in the process of installing decking for the approach bridges. One main stand pier is completed and the other is under construction.”

“At the same time, approach roads are being built for the west side (the Mandan side). The east side approach road (the Bismarck side) will be completed later when part of the existing bridge can be demolished, since the east side will be close to the location of the approach of the existing bridge,” Kopp explained.

The west approach of Liberty Memorial Bridge was demolished so Lunda Construction could begin pile driving for the west approach of the new bridge. “The west end of the new bridge ends up at the same location as the west end of the old bridge so we have to remove the old before the new can be completed,” Kopp said.

“Crews will continue to work throughout this next winter also. The plan is to work on the deck surface, using concrete pavers. We are anticipating completion of the bridge by October 2008,” he added. CEG

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