The Golden Gate Bridge

East Bay MUD

The Mokelumne Aqueducts supply water to more than 1.3 million people living in the East Bay area. EBMUD is nearing completion of a $39 million project to increase the seismic reliability of the No. 3 Aqueduct.

Constructed in 1963, No. 3 has an 87-inch diameter and is the primary pipeline conveying about half the daily customer demand of some100 million gallons per day. Upgrades include strengthening of levees at the pipeline river crossings, reinforcing pipe joints for five miles of buried pipeline, and improving pipe supports for nine miles of elevated aqueduct. The elevated aqueduct upgrade involves the innovative use of elastomeric seismic isolation bearings to mitigate ground shaking effects on the pipeline.

The design incorporates performance-based concepts that allow for repairable damage as long as the performance objectives are satisfied. This approach led to an economical solution saving over $2 million versus a "conventional" design using working stress and allowable pile load criteria. Cost savings results from minimizing the need for expensive and environmentally disruptive foundation upgrades.

The strategy is to allow the pipe to move laterally relative to the ground during an earthquake. Acceptable sources of system flexibility include concrete pile slippage and cracking, and elastomeric seismic isolation bearings. Foundation strengthening is used only where the allowance of flexibility was deemed unfeasible. Upgrades were tailored to the western and eastern reaches of the elevated aqueduct because of the variation in seismic intensity and foundation conditions along the alignment.