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Thu December 16, 2010 - West Edition
Situated in the central part of the state, Utah County is 1,998 sq. mi. (5,174 sq. km) in size. Between 2000 and 2009 the county has seen a 48 percent increase in population. State government officials determined that the population in this area would increase by 250 percent between 2000 and 2030. Additionally, the county has 10,867 non-farm businesses which represents 15 percent of the state’s total.
To accommodate the explosive population growth in this area the Utah Department of Transportation (UDOT) committed to improve critical transportation corridors. In 2002, a transportation study was conducted by the Mountainland Association of Governments (MAG). MAG’s study evaluated needs of both the east-west corridors and the north-south corridor of I-15.
The significant population growth in the area precipitated the state government to accelerate planning and funding to reduce the already congested roadways. Out of this planning and commitment to funding emerged the Pioneer Crossing project.
Pioneer Crossing is a new five lane, 6 mi. (10 km) urban arterial connecting Saratoga Springs to Lehi, Utah. The new corridor also will include a new diverging diamond interchange on I-15 at American Fork Main Street which replaces the existing diamond interchange. Additionally, I-15 will be widened to six lanes in each direction, including an express lane through the interchange.
According to Jose Rodriguez, project lead of the Pioneer Crossing project, UDOT selected the team of W. W. Clyde and Co. of Springville, Utah, and Kiewit Southwest Co. of West Valley City, Utah, in September 2008 to design/build the project. The project, completed in October 2010, cost $264 million.
The centerpiece of the project is the diverging diamond interchange (DDI) at the Main Street intersection with I-15. Rodriguez stated the Kiewit/Clyde team emphasized the cost benefit of the DDI with improved traffic flow and safety, along with the cost savings of accelerated construction techniques through the design build process.
DOT took the bold step in granting approval of this concept along with an accelerated bridge construction technique to minimize traffic congestion on both the interstate highway and arterial roadways.
The DDI is an innovation introduced in Europe and first implemented in the United States in Springfield, Mo., by the Missouri Department of Transportation. The DDI design increases capacity, Rodriguez said, but at the same time enhances safety by eliminating signalized left turning movement at the interchange access points. The end result is a crossover at a signalized point, creating the diverging nature of the interchange.
An extensive public education program was implemented by UDOT to help drivers adapt to the uses and benefits of the DDI, along with providing construction timelines and alerts.
The DDI in Missouri took advantage of utilizing the existing structure and retrofitting it to allow for DDI movements. Rodriguez stated UDOT determined the entire structure would require replacement because of its age. Workshops were held with the Parsons Design Firm of Pasadena, Calif., and UDOT to familiarize all personnel with cost benefits of the DDI, including operational and implementation concerns.
The new structure consisted of a two-span prestressed concrete girder superstructure, which replaced the existing four span structures.
Accelerated construction techniques involved constructing each span off location but within construction site limits. Using short-term roadway closures, the spans were moved into place, thus avoiding the normal long-term delays incurred during conventional bridge construction.
Once final design was completed, construction progressed on the Bridge Staging Area (BSA), while ground preparation occurred at the permanent bridge location.
“Precise elevation and location controls were always maintained to ensure a precise fit when the spans were placed,” Rodriguez said.
The DDI spans were similar to conventional bridge construction with live-load continuity on continuous reinforced deck. Seat type abutments were used at bridge ends supported by pipe piles adjacent to mechanically stabilized earth walls. The center bent was supported by four 8 ft. 2 in. (2.5 m) diameter drilled shafts.
The final superstructure required nine pre-cast, prestressed bulb-tee concrete beams 94.5 in. (240 cm) deep and 190 ft., 9 in. (58.5 m) in length. The deck of each span was cast with a construction joint located 10 ft. (3 m) from the ends of the girders.
Placement of the structures was accomplished using self-propelled modular transporters (SPMTs). The SPMT’s provided a four-point support system thus reducing structure twist during transport. Twist movement was monitored though a relative simple string line system.
Diagonal string lines were placed on the spans that terminated at the SPMT supports. The string lines were monitored during transport by personnel placed on the span and active adjustments occurred as the move progressed.
Transport distance from the bridge farm location to its permanent location was 1,000 ft. (304.8 m). Movement of these girders occurred over two different nights thus avoiding traffic disruptions during the day.
The final setting of the spans relied on precise elevation control established during construction. As the spans were lowered on their permanent bearing locations 18 points of support had to precisely determined.
“Any difference in elevation induced transverse stresses on the bridge desk. In the end all spans were set as planned,” said Rodriguez.
Other project features included the 4.2 mi. (6.8 km) relocation of a 60 in. (152.4 cm) water line for the Central Utah Conservancy District.
Pavement for Pioneer Crossing was 8.5 in. (21.6 cm) plain-jointed concrete pavement on top of 4 in. (10.2 cm) untreated base course on top of 18 in. (45.8 cm) granular borrow.
I-15 pavement consisted of 13 in. (33 cm) of plain-jointed concrete on top of 4 in. (10.2 cm) of untreated base on top of 13 in. of granular borrow. 115, 000 cu. yds. (87,924 cu m) of PCCP was used on the reconstructed lanes of I-15.
22,700 sq. ft. (2,109 sq m) of sound walls are being constructed because of the urban setting.
Additionally, the project provided for new bridges over the Union Pacific Railroad and the Jordan River.
Including the DDI the bridge construction included 9,000 cu. yds. (6,881 cu m) of structural concrete, 900 tons (816 t) of steel reinforcement and 23,000 linear ft. (7,010 m) of steel piling. UDOT provided a financial completion incentive of $25,000 per calendar day up to a maximum of 120 days.
In the end UDOT and the Kiewit/Clyde team completed the second DDI in the nation and the heaviest documented precast prestressed spans moved in place using SPMT’s. The design life for all the new bridge structures is 75 years. Other new bridge structures include the Jordan River and the UPRR crossing at Mill Road intersection. CEG
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