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Complex Interchange On Schedule, Budget

Tue November 22, 2011 - Midwest Edition
Dick Rohland

Lengthening shadows and cooling temperatures are not slowing construction crews rebuilding a major interchange in the southwest corner of the Minneapolis/St. Paul Twin Cities region.

Blessed by a long and dry fall season, road and bridge crews continue to move forward at a good pace and remain on schedule to complete the I494/TH169 interchange despite spring flooding and three weeks of lost time caused by a state government shutdown said Michael Beer, MnDOT project manager.

Located where the suburban Minneapolis communities of Bloomington, Eden Prairie and Edina meet, the interchange brings I494 and TH169 together to split traffic off in all directions of the compass and into the local communities.

TH169 is a major inter-regional corridor that runs from the southwestern corner of Minnesota up through the Twin Cities then straight north to the northern lake vacation area of the state. It is a busy trucking, commuting and traveler’s highway and carries an ADT of 53,000 vpd north of the interchange and 80,000 vpd south of the interchange.

At an ADT of 136,000 vpd, I494 running east from the interchange is by far the busiest in terms of traffic and the communities it runs through. It runs east and west and is the southern segment of the I94 beltline that runs for more than 100 mi. (161 km) around the Twin Cities. East of the interchange it enters the city of Bloomington where it is lined on both sides by businesses, restaurants and retail centers including the Mall Of America and the St. Paul/Minneapolis Airport.

The joint venture of Edward Kraemer & Sons and C.S. McCrossan grabbed the design build contract with a $125 million bid. Edward Kraemer & Sons is based out of Plain, Wis., and C.S. McCrossan is located in Maple Grove, Minn. The companies have 150 years of heavy construction experience between them.

Road crews have their work cut out for them. Working under high volume traffic conditions, workers and their heavy equipment are working in and around tight quarters sometimes within feet of heavy freeway traffic. Drivers hauling materials in and out of the sight are competing for road space with more than 100,000 motorists on a daily basis.

When the new interchange opens in November 2012, motorists will drive through a system of complex ramps, loops and a frontage road system that will seem to flow with perpetual motion. according to an animated MnDOT visualization. Along with the standard freeway loops, new flyover ramps will eliminate at-grade crossings and signal lights that slowed traffic and caused time consuming congestion in the past.

Auxiliary acceleration and deceleration lanes will be added in each direction on TH169 through the interchange to give motorists more space, length and time to exit or access TH169 to help keep traffic flowing and essentially making this part of the highway a freeway

The ramps and loops gliding into and out of mainline freeway traffic will permit six freeway to freeway movements of non-stop, fluid traffic. A half dozen storm-water retention ponds scattered throughout the new interchange will treat runoff from the additional impervious surface that make up the new ramps, highway lanes and frontage road system.

The most dramatic visual change motorists can expect to see are the four flyover ramps that will bring traffic up and over segments of the mainline highway system. These ramps at 1,092 ft. (332.8 m), 966 ft. (294.4 m), 510 ft. (155.4 m) and 121 ft. (36.9 m) in length will replace road movements formerly impeded by the at-grade crossings and signal lights.

Other new features include six roundabouts at key intersections as part of the frontage road that will circle the interchange without interfering with the highway traffic. The road will allow for convenient, local access in and around the neighborhoods of the interchange.

A new bridge connecting Washington Avenue just west of the interchange and crossing I494 will be part of this road system and make an easy connection between local neighborhoods originally cut off by the freeway.

Nine bridges will be constructed along with 27 retaining walls that will go up for this project.

Long in the planning, it is relatively short in terms of construction time for a project of this size and scope. Beginning in November 2010, construction is expected to be completed just two years later in November 2012.

To reach this goal, the contractor will bring in a small army of workers and heavy equipment. An estimated 1,000 construction workers and MnDOT staff will have labored on this project while hundreds of pieces of heavy equipment will eventually roll onto the site according to MnDOT staff.

Looming over and scattered throughout the construction zone are a dozen Manitowoc, Terex, American, Link-Belt and Grove cranes for the lifting operations. An equal number of Cat backhoes of all sizes are digging out tons of soil for soil removals and sewer construction while Cat and Volvo dozers and scrapers roam the site.

Throw in over a dozen Cat, Gomac, Allen and Ingersoll Rand pavers, rollers and drums and there are over four dozen pieces of heavy machinery mixed in with over one hundred tradesmen on the site now.

Safety and congestion spurred the new design and construction of this interchange, Beer said.

“The congestion reports showed that there are three hours of congestion both for the morning and afternoon rush hours. Additionally, local access was mixed on the same signalized ramps as the highway and interstate access,” Beer explained. “And with congestion, you have safety concerns.”

At the same time, the new design will have a ripple effect on traffic congestion at the next interchange a little more than a mile north of the construction site.

“We think the new Washington Avenue Bridge will take some of the pressure off the interchange just north of here at Valley View Road. It has ramps, frontage roads and signal systems that are fairly close to together so there is a lot of congestion there,” Beer noted. “So, anyone who wants to access TH169 or I494 can come down here to the new interchange which should help in alleviating the congestion there.”

At the closing of the first full year of construction, the work on the project has been going well Beer said but not without some major and unexpected hurdles to jump.

The spring flooding of the nearby Minnesota River and the state government shutdown that abruptly halted work last summer forced some major adjustments in the work schedule and traffic control, Beer noted.

“Spring flooding on the Minnesota River closed several of the river crossings west of here,” Beer explained. “TH169 was one of the crossings that didn’t close so there was an influx of traffic here.

“The contractor’s schedule had planned to keep all three existing signals on TH169 in operation so we could have full crossing and left turn movements,” Beer continued. However, “with the increased traffic during the flooding, the contractor converted all the signal systems to right hand, right out only. We also have it secured so drivers really can’t cross the highway.”

To support traffic flow through the right turn movements, the contractor built an additional acceleration lane to help ease motorists into the flow of traffic. It was quite a major change in traffic control but it has worked out well and reduced accidents, Beer said.

Just a couple of months later, the three week lay-off of construction during the prime construction season left the contractor and MnDOT scrambling to revise the construction schedule.

“Originally, the contractor planned on rebuilding both southbound TH169 and northbound TH169 this year but with the state shutdown, it would have pushed construction of southbound TH169 into winter,” Beer explained. “For the safety of the traveling public, the contractor decided not to start work on southbound TH169 until spring. Otherwise, we would have traffic pinched head to head on four narrow lanes and we didn’t want to do that during the snow season.”

Along with the lost time and scheduling changes, the site sits on a wetlands area with high groundwater and poor soil conditions. The contractor designers determined that predicted settlement under some of the spread footings for the retaining wall foundations would exceed contract requirements and they decided to use geo piers to increase the native soil stiffness under the spread footings.

“Most of the soil out here is pretty good but we have areas of trapped organics and peat that have to be dealt with in the design and construction process with pre-loading the soil, improving the soil or utilizing pile supported footings,” Beer said.

Because geo piers use aggregate and vibration for compaction, the aggregate compacts both vertically and laterally at the same time to fill in any potential voids around the column of aggregate according to technical reports. The installation is quick, there is less vibration and it is cost effective, Beer said.

MnDOT also is measuring the stress of the steel pipe piling to determine its structural capacity as it is driven into the ground. This also increase efficiency, Beer added.

The curved, steel beams on some of the flyover ramps have been another design and construction challenge for this project.

“Normally, when you have a curved girder bridge, the piers are built perpendicular or radial to the direction of the girders,” Beer explained. However, “when the bridge crosses over I494 and TH169, the pier caps are parallel with the median so the positioning of the piers is affected which results in a pier cap at a large skew angle to the girders.

“This interferes with the differential length of the inside girder span to the outside girder span. So it is a design challenge but also a challenge to erect these beams during a weekend closure because each beam doesn’t react the same during the erection process because of the span differential and curvature.”

Site size and the large number of sub-contractors make coordination a key to staying on schedule, Beer noted.

Though it is a huge project, the site is small and hemmed in by commercial, light industrial and residential neighborhoods, including Winter Park, the Minnesota Vikings training center.

“It’s sometimes a struggle for the contractor to find large, open areas to work in,” Beer said.” There are 27 retaining walls going up, bridge work and cranes are sometimes in the way of grading operations and about $16 million of utility relocation work that is going on at the same time.”

The quantities show the intensity of the work. 5.2 million lbs. (2.4 million kg) of structural steel will be lifted into place, 102,000 lf (31,000 m) of concrete curb and gutter will be poured and 54,396 tons (49,350 t) will be placed.

Backhoes will dig out an estimated 1,292,400 cu. yds. (987,400 cu m) of common excavation and crews expect to lay 49,126 lf. (15,000 m) or 9.3 mi. of sewer pipe.

And as in other projects of this size, MnDOT also is asking for help from the public to be patient and courteous both to the other drivers on the road and to the road and bridge workers building the project.

Delays and slow downs caused by traffic switchovers, ramp closures and detours can be expected, MnDOT warned along with full highway shut downs during bridge demolitions and beam setting operations.

By the end of this construction season, however, motorists will already see some improvements throughout the site.

“We expect to have northbound Highway 169 completed along with four of the six roundabouts installed on the new frontage road system around the interchange,” Beer said. “The new Washington Avenue Bridge spanning I-494 is also on scheduled to be completed this year. Additionally we have made significant progress in constructing the new flyover ramp from westbound I-494 to southbound Hwy 169.

The winter construction season will bring some short term relief as traffic will be switched back to the new northbound roadway while bridge crews work through the winter on the substructures.

However, next spring, traffic will revert back to four narrow lanes on the new northbound lanes of TH169 while road and paving crews build the new southbound lanes for the highway. By November 2012, though, motorists should see the interchange completely open with much less congestion and increased safety.


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