Locals know the intersection of I-15 and U.S. 95 in Las Vegas, NV, as the “Spaghetti Bowl.” As of May 2000, they’ll have an extra helping of relief with more lanes, ramps and bridges as contractors build a new interchange. With 330,000 cars per day, it’s the busiest interchange in Nevada.
Today’s volume of traffic provided the project’s biggest challenge. “The main criteria was to maintain traffic flows during construction,” said Tom Patton, project manager for Meadow Valley Contractors Inc., an outfit out of Phoenix, AZ, that was the main contractor for the job. “All major ramps were open in the daytime all the way through.”
Working around the traffic called for an innovative approach to construction and tremendous amounts of engineering work. Patton, describing the four major packages of work involved in the job, said the first was for the four segmentally built bridges, which was the first-ever precast segmental bridge project in the state. The 3.6-meter (12 ft.) segments were cast off-site, then assembled with a gantry crane, which made up 25 percent of the contract. Another 25 percent of the project was typical cast-in-place structure work; another 25 percent was grading work. The last 25 percent Patton described as miscellaneous. This all added up to four cast-in-place ramps, three new bridges, three bridge lane widenings, 77,540 square meters (93,048 sq. yds.) of concrete paving on grade, the removal of 1,798 meters (5,933 ft.) of concrete water channel and its replacement with 840 meters (2,772 ft.) of precast double box culvert, and 1,660 meters (5,478 ft.) of cast-in-place triple box culvert.
Besides being a major structural and interchange project, this also was a flood control job. Crews replaced what is known as the “Las Vegas Creek” with a box culvert system, which absorbed approximately $17 million of the project’s $92-million budget. This price tag makes this project the single largest construction contract the state of Nevada has ever completed — 60 percent larger than the next largest state highway project.
Because construction began in December 1997, weather provided additional challenges, as El Nino descended and brought one of the rainiest winters on record in Las Vegas. As crews started their off-the-freeway work, the rain set in. Then they hit groundwater, which made excavation difficult, according to Patton. Elaborate excavation was required on the job, which called for the use of hole rams. “We trenched both sides to get a place to break into,” said Patton.
Access to the site offered another challenge. “We had limited site access and we were limited on property to process materials that came out of the excavations,” Patton said. “We had to lease adjacent land from UP Railroad, who owned it.”
The confined site meant pushing the limits of structural design and constructability. As a result, there are ramps with radiuses as small as 130 meters (429 ft.), crossfalls up to 8 percent and gradients to 7.95 percent.
The gantry crane that assembled the segmental bridges and was designed specifically for this job by NRS/STRUKTURAS in Norway was shipped in pieces and assembled on site.
It was designed for the particular requirements, so it could launch and erect around a minimum curve radius of 130 meters (429 ft.). It also had to be moved from bridge to bridge and be available for commissioning per an aggressive project schedule.
This crane — the first double-articulating gantry truss used in the United States, according to Patton — pushed the envelope of existing segmental bridge technology and allowed work to go on over the top of live traffic. The main truss of the crane is 53 meters (174 ft.) long. The front and rear noses articulate up to 20 degrees. The overall length of the truss with full noses is 135.7 meters (445 ft.).
Joe Schroeder, project manager, Walter Construction, the segmental subcontractor, said he received hundreds of phone calls about its work on the project and about the crane.
Other subcontractors for Meadow Valley included Steel Engineers, Innovative Construction Systems, Las Vegas Paving, Agra Foundations, Barajaf Associates, Amalgamated Safety, Desert Construction and Penhall Company.
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