Precast Solutions - Winter 2009 - (Page 17) snaking into complex curves,” says Carlo Cattelan, Technopref’s project manager on the Connector. Cattelan oversaw production of the concrete segments along with Fred Esch, Technopref’s general superintendent. “It’s a short tunnel with a complicated alignment.” Just one of the two concrete tunnels to be built under the river for the Connector has been completed, but all of the 1,120 ring segments already have been produced. Since there is little room on the work site for storage of the segment rings, delivery occurs in conjunction with the mining in a “just-in-time” fashion. Depending upon the need, A.C. Miller ships by tractor-trailer an average of eight to 10 rings per day to the site when the tunnel-boring machine is mining. At its peak, the company delivered 16 rings to the site in one day. Initial meetings with three local concrete manufacturers quickly led Technopref Industries to zero in on A.C. Miller. But before the company could meet the expected demand of producing and delivering many concrete segments daily, it had to upgrade its Blairsville facility and hire more workers. The company also made $800,000 in improvements to the plant and, to bolster its staff of 60 at the facility, it hired 40 more workers specifically for the Connector project. The A.C. Miller/Technopref partnership has been very successful, says Paul Zick, project director for the North Shore Connector. The two companies achieve a high level of precision in manufacturing the 11-inch-thick segments for the 20-foot-diameter, 4-foot-long rings. The structural and dimensional integrity of the rings is important, since the mining process and the life of the product depend on it. “The attention to detail was tremendous,” Zick says. “On the segments, the important part is the tolerances. The pieces have to be interchangeable. If, during installation, you damage a piece from one ring, you should be able to replace it with another piece from a similar ring – even if the dimensional tolerances on the segments is less than one-sixty-fourth of an inch.” Cattelan says Technopref’s history of working with tunnels gives it an advantage in the market. “This job is about precasting, precision, consistency, high-quality manufacturing standards, and having knowledge of what goes on with the tunnel boring machine (TBM). You need to be mindful of how the TBM works and how the TBM staff wishes to operate. You always have to give the highest priority to product tolerances,” he says. After delivery to the work site, the ring segments must then be moved into position for installation. In some tunneling operations, a rail line would carry them into the tunnel. Such a construction transport method was impossible for the Connector, however, because of the grade of the tunnels. Custom-built flatbed wheeled vehicles (nicknamed “skateboards” by the mining crews) are being used instead. At the site access shaft (known by workers as the Launching Pit), the installation process begins with lowering the ring stacks onto the skateboards that cart the ring stacks into the tunnel, to the docking station and to the TBM. At the docking station, hydraulic equipment lifts the segments onto a “sled,” which carries them toward the TBM erector. TBM crews then operate the ring erector machine’s hydraulic arms to assemble the segments into a ring. Workers then use pneumatic impact wrenches to bolt the ring into place. The TBM drives itself forward by pushing off the rings that are installed. “The TBM puts 8 million pounds of pressure on the rings while pushing itself,” Buchan says. Once assembled by the TBM erector, the segment rings, along with compressed gaskets, are held together with bolts and dowels. Partnership continues The partnership between the two companies has gone so well that they are working together on a second project, a subway line in New York City. SPIN-N-LOK™ XT THE PRECAST SHOW BOOTH 1429 Intricate process The rings are made of a much more sophisticated mix of concrete than the type used for roads, says Mike Buchan, vice president of A.C. Miller Concrete Products. “Its compression strength is very high, attaining up to 12,000 psi in compressive resistance with very low permeability to water,” he adds. The concrete used for the rings is comprised of portland cement and silica fume. When mixed with cement, the silica fume powder gives the mix added strength and density. The rings are cast in forms that were manufactured in France specifically for the Pittsburgh job. At the end of the production process, the segment rings are cured in a • 10,000 lbs CAPACITY • GREATER RANGE OF MOTION • ONE-POINT PICK CAPABILITY CONCRETE PIPE AND MANHOLE LIFTER 1-800-423-4425 • americandrillbushing.com Winter 2009 | Precast Solutions 17 www.precastsolutions.org http://www.americandrillbushing.com http://www.precastsolutions.org
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