Lake Mead, Third Intake Structure

Abstract

This project considers the Lake Mead third intake shaft. The third intake shaft was commissioned by the SNWA in order to provided continued access to clean water for the Las Vegas Valley in light of a recent trend in dropping lake levels. At present data shows that Lake Mead is at only 46% of capacity, and this level is expected to continue to drop. Indeed, if the lake level drops only 114 ft both the first and second intake systems will be non-functional (the lake level has already dropped 110 ft in the period between 2000-2008.) The contract for this project was awarded to Las Vegas Tunnel Constructors; we have been asked to design the intake shaft and starter cavern for this project. The Lake Mead third intake shaft is to be 600 feet deep and 32 feet in diameter. The shaft includes two stub tunnels: one for the support of the Tunnel Boring Machine used in the excavation of the tunnel, and one for a future connection to the other two intakes. At the bottom of the intake shaft will be a large excavated starter cavern for the construction of the Tunnel Boring Machine which is 200 feet in length, 45 feet wide, and 30 feet tall. On the opposite end of the cavern from the tunnel extends a maintenance stub tunnel (25 feet in length and 20 feet in diameter.) This report will provide the design specifications for these tunnels as recommendations to Las Vegas Tunnel Constructors, and will also briefly discuss the use of the Tunnel Boring Machine (TBM) which will be employed for the construction of the intake tunnel under the lake.