It isn’t quite the “journey to the center of the Earth” envisioned by Jules Verne, but it’s not far off.
The Lake Mead Intake No. 3 Shafts and Tunnel Project, in Boulder City, NV, is the world’s deepest subaqueous tunnel. Its many achievements made it one of six projects honored as finalists for the 2016 ASCE Outstanding Civil Engineering Achievement Award.
The project, in conjunction with the Low Lake Level Pumping Station now under construction,
will safeguard the current capacity of the Southern Nevada Water Authority against extremely low lake water levels that would knock out two higher-level existing intakes. It also allows the authority to draw higher quality water from a deeper, more desirable intake location. Lake Mead supplies 90 percent of the Las Vegas Valley’s water.
“We gathered a team of people who had experience tunneling in difficult conditions,” said Marc Jensen, SNWA director of engineering. “And we not only used the experts available to us through our design team, but we pulled in our own independent experts and asked them to participate in the discussion about how we were going to meet these challenges, and specifically how to assess the risks associated with such a challenging project.”
That’s not to say there weren’t nerves. Jensen can pinpoint the exact day when the project turned the corner from stress to success – Dec. 10, 2014.
“We holed through to the intake structure,” Jensen said.
Project Manager Erika Moonin added, laughing: “I remember Marc saying he can finally sleep now. That was one of the higher-risk components of the project, tying into the intake structure and being on target.”
See a video about the project, as presented at the gala:
The Vegas Tunnel Constructors team used the innovative approach of installing a prefabricated intake structure under the lake bed using immersed tube techniques to mitigate the risks inherent to construction under more than 300 feet of water. A 23-1/2 foot diameter tunnel-boring machine excavated three miles under Lake Mead through a mishmash of highly fractured metamorphic and volcanic rocks subject to more than 13 bar of water pressure to dock with the intake structure precisely on target.
“We have very difficult ground conditions, extremely variable and notoriously challenging,” Moonin said. “This whole area is very complex geology.”
Jensen and Moonin both praised the construction team of Salini Impregilo and S.A. Healy.
“They really needed to be innovative during the construction because there were conditions that they ran into that haven’t been dealt with before,” Moonin said. “So it was really [being] on the fly in the field, having their engineers work together with their field folk to come up with ways to handle the challenges they came across, that made the project so successful.”
ASCE’s annual OCEA Award honors projects that best illustrate superior civil engineering skills and represent a significant contribution to civil engineering progress and society. Honoring an overall project rather than an individual, the award celebrates the contributions of many engineers.
ASCE will announce the winning OCEA project at the Outstanding Project And Leaders Gala, March 17, in Arlington, VA. The evening also honors this year’s group of OPAL winners, as well as recipients of the Charles Pankow Award for Innovation, the Henry L. Michel Award for Industry Advancement of Research, and the ASCE Excellence in Journalism Award.
Read more about the Lake Mead Intake No. 3 Shafts and Tunnel project at the ASCE Library.