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SDDOT Widens I-90, Exit 61 in Rapid City

Wed April 09, 2008 - Midwest Edition
Dorinda Anderson

Increased traffic numbers partially due to heavy tourism, spurred the need to widen the existing 30-ft. (9 m) wide overpass at Interstate 90 and Exit 61 at Rapid City, S.D. It will be widened to 205-ft. (62 m).

The South Dakota Department of Transportation (SDDOT) awarded the Interstate 90 Exit 61 construction project to Stanley J. Johnsen Concrete Contractor Inc. of Rapid City.

The two-year $16.5 million project began on March 5, 2007, and is scheduled to be completed July 25, 2008. The entire interchange is being reconstructed, including a new bridge over Interstate 90 to include MSE walls and four new ramps.

A 1.3 mi. (2 km) stretch of Interstate 90 will be replaced, and a 0.7 mi. (1.1 km) portion of Elk Vale Road will be replaced.

“We built a single-point urban interchange on top of the bridge, which includes four driving lanes, two in each direction, and two turn lanes, creating a six lane configuration,” explained John Gerlach of the South Dakota Department of Transportation. Previously the exchange was a diamond shape that included one lane in each direction with a 4-ft. (1.2 m) shoulder and no turn lanes; it was built in the 1960s.

According to studies done in 2004 prior to the start of this ongoing project, about 8,700 vehicles travel over Exit 61 and traffic on I-90 reaches about 27,000 vehicles each day, so the new configuration will be much safer, Gerlach said.

“We don’t have any projected traffic numbers for the future but we are expecting numbers to increase.”

In addition to being a rapidly growing community with a population of approximately 70,000, Rapid City also is a popular tourist location, being situated in the heart of the Black Hills and close to Mount Rushmore.

The whole area along the Interstate 90 at Exits 60 and 61 is seeing extensive development of businesses and so a huge influx of traffic is anticipated, explained Dave Buck of Stanley J. Johnsen Concrete Contractor Inc., requiring a new truck bypass from Interstate 90 to Highway 79.

The 2007 phases of construction were part of an ongoing project to construct a new southeast connector route in Rapid City, S.D., which began in 2005. Construction in 2005 and 2006 made it possible for traffic to enter or exit I-90 from Exit 60 in both directions. The project required the removal and reconstruction of eastbound and westbound I-90 between LaCrosse Street and about half way between Dyess Avenue and Elk Vale.

Concrete paving on Elk Vale Road and Mall Drive north of the bridge was completed by Aug. 1, 2007, 21 days ahead of schedule. Westbound lanes were completed and traffic was restored on the new concrete paving, Gerlach explained. Four lanes of traffic were opened — two lanes westbound and two eastbound and the bridge was completely decked.

Since the project was going so well, prime contractor Stanley J. Johnsen started work on the north side of Elk Vale Road and completed it last fall. It wasn’t scheduled to be completed until spring 2008.

“Before we started this portion we had to guarantee the DOT that we would get it done by snowfall,” Buck said. “There is a big truck stop on that north side [of Elk Vale Road] and so we had to get it done [so trucks could use the road during the winter.]”

Bridge construction resumed about two weeks later, about mid-August after the annual Sturgis Motorcycle rally, a time when approximately a half million motorcycles travel the region. Sturgis is only about 25 mi. (40 km) from Rapid City.

“For safety, all construction has to be shut down and roads opened to normal traffic patterns during the rally,” Buck said.

Work on the next phase of the interstate also began on Aug. 13, 2007, at which time traffic on the interstate was put head-to-head on the newly reconstructed westbound lanes, so reconstruction of the eastbound lanes could begin.

The grade on the interstate had to be lowered about 7 ft. (2.1 m) because the overpass needed to be lowered to reduce the former steep profile of the road to a more gradual slope, Gerlach explained. Contractors used 637 and 631 Caterpillar scrapers, dozers from D6 up to D10, and Caterpillar 330 and 325 excavators and one 375 excavator to get the work done. Several 140 motorgraders also were used.

Construction of the roadway required two different depths of concrete, 12 in. (30 cm) on the on- and off-ramps, and 9.5 in. (24 cm) on the overpass roads, Gerlach said. The difference was required because of the varying traffic volumes. The roadway required about 100,000 cu. yd. (76,500 cu m) of concrete, which included the overpass roadway, ramps to the bridge and the interstate.

“On the bridge, we installed MSE retaining walls for bridge abutments,” Gerlach said. “We had 13,000 square feet of wall; they are fairly long, about 400 feet each.”

American 80-ton (72.5 t) cranes were used for the bridge work, along with deck finishing machines by subcontractor Bid-Well of Canton, S.D.

During the 2006-07 construction season, some unusual soils were encountered on the interstate that caused scrapers and dozers to get stuck, making it necessary to remove about 700,000 cu. yd. (535,000 cu m) of the silty soil and replace it with geo grid and shot rock that is 6-in.-plus (15 cm plus) in size, Gerlach said.

Buck added that the soil was very soft and mucky so new materials were placed to a depth of about 3 ft. (0.9 m) all the way across the roadway for about a 2,000 ft. (610 m) length. Workers used big Cat scrapers to remove it.

“Time wise, it hurt us a little; we lost a few days because of that but we just keep forging ahead,” Buck said.

“Overall this has been a difficult job, but we managed to get through everything and have earned some early completion concessions,” Buck explained. “The job as a whole has gone well. We have been able to keep the traffic running smoothly and we have kept all the businesses open. We have a good group of subs that play a big part in that.”

Work for the 2008 construction season began the first week of March, where projects that were started in 2007 are being completed, including completing MSE wall work, bridge work and Elk Vale Road work.

Traffic control was set up the first week of March along with asphalt milling so that by the second week of March bridge deck pouring could continue on Phase 3, Buck explained.

Even though temperatures are hot during the day, nighttime temperatures remain cold enough that cold weather protection is required, meaning the pour is covered at night and artificial heat is used to keep the deck warm.

To complete the bridge deck, five phases will be incorporated since the bridge is about as wide as it is long, Buck said. The first two phases were completed during the 2007 season so traffic could be maintained over the existing bridge.

Once the new part of the bridge was completed, the traffic was switched to the new part so demolition could take place to remove the existing bridge.

To pour the concrete, pavers and placer spreaders were used. Stanley J. Johnsen has its own batch plant to produce its own concrete.

“We set up the plant onsite; it is a lot cheaper than buying commercial ready mix and we don’t have to haul it as far.”

The plant can be moved, downtown and set up within four to five days.

“We figure about a week to move it and tear it down and set it up,” Buck said.

To save on materials, Stanley J. Johnsen uses a reclaimer to use the existing concrete as a base, Buck added.

This final phase is expected to be completed by its July 25 deadline, Gerlach said. CEG

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