Moving ahead
Third 'Stack' phase becomes one of largest MDOT projects in history

By Angelle Bergeron

Kenneth Collins recalled working on designs for the four phases of "The Stack" in Jackson, Miss., when he first joined Michael Baker Engineering some 20 years ago, a telling commentary on the longevity of the Mississippi Department of Transportation project.

"Baker designed all four parts of the original Stack contract," Collins, a project manager with the company's Jackson office, said. "It was the second or third job after I joined Baker."

After waiting all these years for his designs to be implemented, he is excited to finally see the fruit of his labors.

"You design a lot of bridges and a lot of times you never see them," he said. "For this to be going on in our back yard is pretty unique and I think it will help a lot."

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The Stack, so called because it is the only multi-level Interstate/highway interchange in the state of Mississippi, was designed to alleviate the traffic flow within the confluence of Interstates 20 and 55 and U.S. Hwy 49. Following construction of the interstate system through the Jackson area, traffic (specifically on the east/west I-20) increased dramatically with the growth of the city and daily commuters.

Likewise, truck transports traveling north and south through Jackson on either US 49 or I-55 increased, creating bottlenecks on the stretch of I-20 between the two.

The $58 million Stack Phase III, now under construction, represents one of the single largest projects ever tackled by MDOT.

"Not only is it one of our biggest projects because of its size, but also because it is in a large metro area with a large amount of daily traffic," said Amy Frederic, special projects officer with MDOT's external affairs division.

The contract for The Stack Phase I was let in 1992 and Phase II followed in February 1997. Phase I included construction of a section of southbound I-55 from the Pearl/Pascagoula Street exit to I-20, said Frederic. Phase II involved the widening of the northbound I-55 bridges over US 80 in Pearl River and overlaying of pavement from I-20 to the Pearl/Pascagoula interchange.

The Stack Phase III was awarded to Hill Brothers Construction & Engineering Co. Inc. in November 2002 and the company began work in March of this year.

"The contract is among the largest single contracts ever awarded to Hill Brothers," said Paul Leonard, project manager. "Although we have completed projects on I-55 and various other projects throughout the state, this is the biggest."

The project includes the reconstruction of more than five miles of I-20, I-55 and US Highway 49 and construction of a new fly-over bridge connecting the three roadways.

"The ultimate goal is the elimination of a lot of weaving of traffic from 49 northbound and I-20 westbound to I-55 northbound and I-20 westbound," said Collins, whose firm won the CE&I (construction, engineering and inspection) contract and is overseeing daily construction for MDOT.

Currently, traffic traveling northbound on US 49 desiring to continue north on I-55 must make a loop to I-20 westbound and then weave across two lanes to connect to I-55, Collins explained. Likewise, those traveling I-20 westbound and desiring to take I-55 northbound must weave across one lane to take the I-55 exit.

"It's fairly unique because U.S. 49 is flying over interstates and ramps and coming back to the other interstates," said Freddie Stokes, assistant district construction engineer of operations for MDOT. "People will no longer have to jockey for position to switch lanes."

Stokes, who oversees project field offices for MDOT in central Mississippi, said he is treating Michael Baker as another field office that is handling all the day-to-day operations.

"Things are flowing real well on the project," said Stokes. "The contractor is doing an excellent job. He's on top of everything. It's been rather pleasant for a project of this size to go as smoothly as it has."

Hill Brothers' contract includes the construction of seven bridges, an asphalt and concrete roadway, and drainage that consists of box culverts, pipe, box-bridges and inlets.

The majority of the work, which was designed outside of existing traffic to reduce impact, is being done during the day, Stokes said.

"When we actually do the part over the interstate, we will have to do rolling lane closures for setting beams, etc. and will probably do that at night," he added. "That will only be a short duration compared to the entire life of the project and won't be until the end of 2004 or later," he added.

Still, a buffer zone was created between the traveling public and the work area, using concrete median barriers. Provisions for traffic control and service patrol are included in the Hill Brothers contract.

"Hill Brothers has implemented the Baker/MDOT pre-determined traffic control plan," Leonard said. "However, coordination of the plan with the construction methods is the greatest challenge we've encountered to date on this project. As the traffic control plan designates our work areas, Hill Brothers broadcasts a construction work schedule via a Web address to modify and alert the public of future and current lane closures."

In addition to lighted signs (on the boundaries of each edge of the project) that alert motorists of upcoming construction and speed limits, Hill Brothers has implemented a service patrol for the duration of the project. A tow truck monitors the construction area round the clock and is available, at no expense to motorists, for any problems. The free service also provides tows of abandoned vehicles to a designated place in an effort to keep medians safe.

"The service patrol has been very helpful, and MDOT has received many compliments and positive feedback," said Frederic.

Because the plans were old, Michael Baker Engineering did some updating before construction began on Stack I and II. The same was required on this third phase, and Collins participated in the design changes.

"Originally, the interstate pavement was not to be replaced, but since so much time has passed it was decided the pavement (on portions of I-55 only) was so bad that it did need to be replaced. That affected the traffic control plan," Frederic said.

Actually, the original designs, rather innovative at the time, are still considered quite an effective solution.

"There are about six bridges involved, all complicated geometrics with a basket weave of two ramps requiring a straddle bent design that's somewhat complicated," Collins said. "Where the two roads cross at an acute angle, and one that spans another, you have to have a bent that straddles the road beneath."

The steel-span design, however, reflects a simplistic solution to maintaining traffic on I-20 when placing the girders.

"If it was something requiring forming, it would take longer," Collins said. "This also reduces the amount of down time on the interstate. All lane closings are at night and on weekends and our goal was to maintain all lanes of traffic while construction is going on."

A special 12-hour set concrete was needed in a few portions of the project in an effort to impact traffic flow as little as possible. Whereas the original designs called for four lanes of traffic on I-55 northbound, "we squeezed in five lanes and reconfigured the number of lanes merging from 49/I-20 traffic," Collins said.

For the seven steel span and concrete girder span bridges included in the project, Hill Brothers used approximately 19,000 cu. yds. of structural concrete, along with 91,000 lin. ft. of concrete piling, said Leonard.

"The project also included 800,000 plus cu. yds. of borrow excavation, 90,000 sq. yds. of concrete pavement, 150,000 plus tons of asphalt pavement and approximately 2 mi. of drainage structure," he added. "In addition, subcontractor Superior Asphalt has designed a low-rut, 9.5-mm polymer modified surface mix specifically for the Highway 49 and frontage road sections of the project, which are areas that receive large amounts of heavy traffic."

The Stack Phase III is scheduled for completion in December 2006 and Hill Brothers is on schedule.

"I think Hill Brothers is doing a great job," said Collins. "We've got a great relationship with MDOT and it has been a success all the way around."

So far, it hasn't even been determined whether Michael Baker will update the Phase IV plans or not. However, the contract for construction on Phase IV is scheduled for bid October 2007.