Riachuelo 3 The Tunnel

283 Lake Mead intake N. 3 tunnel A s a result of a sustained drought in the south west of the United States, and to maintain the existing water capacity in Las Vegas Valley, the Southern Nevada Water Authority built a new deep-wa- ter intake (Intake N°3) in Lake Mead. The project, constructed by the same contractor of the Riachuelo Outfall Tunnel, included a 611 feet deep onshore shaft, a tunnel of 4.7 km length and marine works for forming a submerged water intake. It was one of the most technically challenging projects in the tunnel industry due to the highly complex geo- logical conditions and to the fact that the tunnel was excavated with a water pressure never faced by a TBM before. The reception chamber is located in the middle of the lake at a depth of over 377 feet. The project included design and build of the following structures: . A 15,000 feet long diversion rock tunnel with covers from 587 feet (at launch) down to approximately 30 feet when entering the reception chamber. . A TBM designed to counter 17 bars water pressure or 40,000 gallons per minute. . A 30 feet ID, a 611 feet deep access shaft. . A mined tunnel from the access shaft, 400 feet deep and 83.5 feet long. . A 200 feet long TBM launch chamber in the lower part of the access shaft. . An 85 feet long connection tunnel and a rear diversion tunnel.