Spring has yet to arrive in the high desert mountains around Salt Lake City. With concrete paving operations still suspended, work on the huge I-15 highway reconstruction project focuses on structures and bridges for interchanges. This puts cranes to the forefront of operations.
Three major interchanges part of the complete demolition and reconstruction of a 27km long stretch of the north-south Interstate highway as it runs through Utah state. They link the I-15 to the east-west I-80 Interstate, and also to a loop Interstate, the I-215. A number of smaller city road connections are also needed.
“Altogether,” says Scott Palmer, a checking engineer with consultant Parsons Brinckerhoff, “the job has involved demolishing 135 bridges. Along with extra ones to increase the number of railway grade separations, we are building 142 bridges, up to 500m in length.” Nearly 50 of the more complex curved bridges are in steel, some of the wider overpasses use long post- tensioned concrete beams and the rest are in precast reinforced concrete. Beams weigh up to 150t.
Some 30 mobiles cranes are at work, supplemented by others coming in and out according to need. Steelwork subcontractor Olsen-Beal has a Manitowoc M250. Other Manitowocs are deployed by the main contractors, including 2250s, 777s and 222s. Grove RTs and truck cranes are also much in evidence.
All this work comes as the project gets to the end of its third year. Work is beginning to have beneficial effects as new interchanges open and sections of the upgraded and widened highway become usable for traffic. It was not always so, and demolition of the 25 year dual three lane highway at the beginning caused delays and widespread local upset. “People now see the benefits,” says Mike Mower, spokesman for Wasatch Constructors, the contractors consortium doing a $1.6bn reconstruction for client the Utah Department of Transportation (UDOT). Some 85 of the 142 new bridges are now ready.
The consortium, a joint venture of Washington Contractors (formerly Morrison Knudsen), Granite Construction and Kiewit Construction Company, gains important flexibility by handling city traffic planning itself, part of an unusual and precedent-setting design and build framework for its huge job. The main condition is that it keep at least half the freeway lanes open throughout daylight hours.
Much responsibility is handed over to the contractor, including most of the design work, quality control and quality assurance and even aesthetics.
“The project was always going to be painful for the population – this road is the backbone of the valley,” says Dave Nazare, technical support manager for UDOT. “But we asked early on what people preferred and the answer was always to get it over with as soon as possible,” he says.
The project could not be avoided. When work began in April 1997 the old highway was found to have crumbled in places. It could not handle the traffic. The Salt Lake City valley is the most densely populated area in Utah with a population of 1.8m and the highway is a crucial freight route from Mexico to Canada. And the Winter Olympics are coming to town in 2002.
The job involved rebuilding the interchanges, and laying 650,000m3 of concrete for paving the 330mm-deep main slab stretching over five lanes of traffic each way. As the valley is an old lake bed, soft alluvial clays and silts are hundreds of metres thick and substantial soil remediation is needed.
Wasatch’s designer, a joint venture of consultants Sverdrup Civil and De Leuw Cather has used methods like stone column ground treatment for some of the higher flyovers. Crane mounted vibrators compact added stone into columns 20m deep and approximately 800mm wide which can bear load when surrounding ground is seismically liquefied.
Foundations for the bridges involve some 16,000 steel pipe piles up to 45m deep. A number of big pile driving rigs mounted mainly on Manitowoc machines drive the 300m to 600mm diameter piles, lift in reinforcement cages and fill them with concrete.
Work finishes in July next year. On Cottonwood sector, the southernmost of three into which the work is divided, they are already planting the salt resistant desert trees that will landscape the future road, and fibre optic is going into the ducts for the traffic control systems.
