Concluding a 3-mile journey that began in 2011, a tunnel boring machine (TBM) excavating Southern Nevada’s third water intake beneath Lake Mead reached its destination today when it "holed through" the concrete intake riser structure that was secured to the bottom of the lake in 2012.
"This is one of most complex and challenging tunneling operations ever attempted; therefore, today is a significant milestone for this historic project." said Southern Nevada Water Authority (SNWA) General Manager John Entsminger. "Coupled with a future pumping station capable of withdrawing water, even at extremely low lake levels, the new intake system helps assure a dependable supply of water for future generations of Southern Nevadans."
Lake Mead Intake No. 3 substantially increases the reliability and flexibility of Southern Nevada’s water treatment and delivery system. Combined with the low lake level pumping station that is currently under consideration, the new intake enhances the SNWA’s existing intake system, enabling Southern Nevada to continue accessing its water resources in Lake Mead, even if lake elevations drop too low for Hoover Dam to release water to downstream users.
Vegas Tunnel Constructors—a joint-partnership effort between two world-renowned contractors, Impregilo and S.A Healy—was contracted to perform the work on behalf of the SNWA. The project included the construction of the 20-foot diameter concrete-lined tunnel extending three miles through complex and variable geologic features under the lake; construction of a 100-foot tall intake riser structure installed on the bottom of Lake Mead; a 600-foot deep access shaft; and additional underground connections to link the intake to the SNWA’s existing water intake system.
"Constructing a project of this magnitude certainly brings unique challenges," said, Erika Moonin, SNWA project manager. "This is a significant accomplishment for the entire project team. The field crews deserve special recognition for their hard work and dedication; they work in difficult conditions and consistently bring their best each day."
The world record-setting project, which encountered the highest water pressures of any tunneling operation to date, still has several remaining activities before the project is complete. These include sealing the connection between the intake tunnel and riser structure; disassembling the 24-foot diameter, 600-foot long TBM and removing it from the tunnel; and installing smaller utility pipelines within the tunnel.
Approximately 2,400 concrete rings—each weighing more than 32 tons—were installed to line and reinforce the excavated tunnel. The rings were lowered underground in six segments, which were then assembled behind the TBM as it advanced.
Construction of Lake Mead Intake No. 3 was initiated in 2008. The project is scheduled for final completion in 2015.
Copyright © 2014 Southern Nevada Water Authority