Crews assembling TBM for first ever tunnel under San Francisco Bay

What about the BART you may be wondering. Well, the Bart is not really a tunnel but a precast tube that was sunk and rests on the bottom of the bay. This water supply tunnel will be part of the Hetch Hetchy system that presently consists of steel pipes constructed some 75 plus years ago that are vulnerable to an earthquake by any one of the bay area faults. If such an event occurred, parts of the bay would be without water for up to 60 days.

This tunnel will be 13 feet in diameter with a concrete lining and a 9 foot diameter steel pipe inside. It will take until 2015 to complete the 5 mile tunnel that will supply water to over 2 million people. It will be designed to withstand a magnitude 7.5 earthquake at a price tag of $313 million. [Source: San Jose Mercury News]