The Seismic Upgrade of Bay Division Pipelines

A Critical Upgrade Beneath A Highway
By Bryan Dessaure and John Prete | February 2014, Vol. 69 No. 2
View inside the slipline work area.

This essential construction project is taking place where the two pipelines cross Traces A, B and C of the Hayward Fault, directly under a major traffic corridor at the intersection of I-680 and Mission Boulevard in Fremont. SFPUC engineers determined that a major earthquake on the fault would damage one or both of these two major pipelines.

As initial protection against this possibility, the SFPUC constructed pipeline shutoff stations on either side of the fault in 2007, providing operators with the capability to shut down the pipelines between the two stations in the event of an earthquake. While these shutoff stations substantially reduced the possibility of flooding to the adjacent residential and commercial area in the event of a break, seismic retrofits of the pipe system itself were still necessary to ensure continued water delivery to the Bay Area.

The most active trace of Hayward Fault, Trace B, could produce a horizontal displacement of up to 6.5 feet, breaking both of the existing pipes. The challenging 45-degree angle at which the pipes cross the fault trace would result in the pipelines experiencing compression and rotation forces during fault movement. Pipe strengthening will also be necessary at nearby smaller traces A and C. The resulting construction project employs a range of materials and engineering solutions, and will cost a total of $78 million to complete.

Sheets of white PTFE are affixed to the bottom of a segment of Bay Division No. 4.
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“From an engineering perspective,” says Wade, “BDPL3&4 Seismic Upgrade is certainly one of our most challenging and interesting projects.”

One particular challenge for this project has been working beneath Fremont’s busy Mission Blvd. This active city street is a busy commuter corridor and the closest crossing between the I-680 and I-880 freeways. The existing BDPL No. 3 crosses Trace B of the Hayward fault beneath Mission Blvd. Here, a complex 305-foot long articulated concrete vault is being installed to protect the pipe at the most challenging earthquake fault trace.

To minimize traffic impacts, the SFPUC and construction contractor Steve P. Rados Inc., are coordinating a phased traffic management plan with the California Department of Transportation and the city of Fremont. The contractor will re-align Mission Blvd. multiple times in order to work beneath the road’s original alignment without causing road closures. As part of this project, they are constructing and demolishing a series of temporary bridges across Mission Blvd. and the two northbound I-680 on-ramps.