Southern Nevada’s Water Authority recently unveiled its newest megamachine: a $25-million custom-made hybrid tunneling-boring machine that operates in both the open and closed positions, meaning the drill face is pressurized for more efficient ground and water control. It took Schwanau, Germany-based Herrenknecht AG 17 months to design and manufacture the 1,500-ton, 600-ft-long TBM, which is being used as part of the third raw-water intake tunnel project at Lake Mead. The additional straw is needed since lake levels have dipped 110 ft since 2000, leaving it at half capacity. In March 2008, SNWA awarded a $447-million design-build contract to Vegas Tunnel Constructors LLC, a joint venture of S.A. Healy Co., Lombard, Ill., and Impreglio S.p.A., Sesto San Giovanni, Italy. The project’s workhorse is the TBM, which will have a trailer and an accompanying crane that installs 2,500 supporting concrete rings, each weighing 3,500 tons. Each ring consists of six separate precast pieces; the contractor expects to average five rings per workshift. Although the TBM has only one operator, a dozen trained support people are needed to ensure smooth operation. The machine was shipped in five large pieces to Long Beach Harbor and then transported to the southern Nevada jobsite via 61 heavy-duty trucks. It took months of planning and coordination to map the route and secure the special permits. It will take four months to assemble the TBM underground, with operation anticipated to start this summer. Components will be lowered down a 32-ft-dia., 600-ft-deep access shaft using a custom-made 50-ton crane and assembled into place with a jack-and-rail system. The TBM will carve out a three-mile-long, 20-ft-dia reinforced tunnel under the lakebed, removing 260,000 cu yards of material in the process. The intake tunnel has a 1,571-day project schedule that is expected to finish in July 2012.
