How do you replace two regional water delivery pipelines that run directly underneath a major interstate freeway and lay across an active earthquake fault?
This is the unique construction and engineering challenge that the San Francisco Public Utilities Commission (SFPUC) is facing during the current Seismic Upgrade of Bay Division Pipelines (BDPL) Nos. 3 & 4 project.
Each day, water from Hetch Hetchy Reservoir in Yosemite National Park travels by gravity through a regional system of pipelines to people and businesses in the greater San Francisco Bay area. This water journeys 167 miles and crosses three active earthquake faults along the way. In the event of an earthquake, a break could sever this liquid lifeline, resulting in an interruption to water delivery for customers that could last for days, weeks or even months.
In 2002, the SFPUC approved the $4.6 billon Water System Improvement Program (WSIP) to repair, replace and seismically upgrade aging pipelines, tunnels, reservoirs, pump stations and storage tanks, thereby improving the system’s reliability for 2.6 million customers in the Bay Area.
“It is just a matter of time before the next major earthquake hits the Bay Area, so we are literally in a race against time to safely rehabilitate and upgrade our extensive water infrastructure so that we can continue to provide reliable water service to our customers in the Bay Area,” says Water System Improvement Program Director Dan Wade.
The project’s proximity to a busy commuter interchanges poses unique construction challenges.
In all, the WSIP includes more than 80 projects spanning seven counties from the Central Valley to downtown San Francisco, and is currently 80 percent complete. One of these projects is the Seismic Upgrade of BDPL Nos. 3 & 4. In a compact half mile area in Fremont, this project will employ an impressive array of construction and engineering solutions.
Crossing the Hayward Fault
Installed between 1952 and 1967, the original Bay Division Pipelines Nos. 3 & 4 are two of four major regional transmission pipelines that currently deliver water from the SFPUC’s regional system and Alameda Creek Watershed facilities to the San Francisco Bay Area. BDPL Nos. 3 & 4 are 6.5 and eight-feet in diameter respectively, extend mostly underground for 34 miles around the south end of San Francisco Bay, converge at the Stanford Tunnel in Palo Alto and reconnect with BDPL Nos. 1 & 2 at the Pulgas Portal entrance to the Pulgas Tunnel just west of Redwood City.
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.
“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.
Innovative sliplining approach
While Mission Blvd., a surface-level street, can be re-aligned in order to work on the complex construction work at Trace B, I-680 cannot be re-aligned or closed to work on Trace A. Thankfully, Caltrans installed a 114-inch diameter, 350-foot segment of corrugated metal pipe (CMP) next to BDPL Nos. 3 & 4 when the highway was constructed in 1969, based on speculation that an additional water line may be needed in the future. In 2013, a new 78-inch diameter BDPL No. 3 pipe was welded and then sliplined into the CMP using a wheel and rail system.
For the parallel BDPL No. 4 pipe beneath the I-680, 400-feet of new 80-inch diameter pipe has recently been installed inside the existing 96-inch pipeline. The designer of record, URS Corp., specified a novel strategy for the sliplining of BDPL No. 4. Workers attached sheets of PTFE (polytetrafluoroethylene) to the bottom of the inside of the existing pipe and the bottom of the outside of the new pipe. PTFE’s low coefficient of friction allowed the pipe to be slipped into place without using rollers or damaging the pipe coating. The PTFE serves a dual purpose in addition to being used for sliplining. Since the annular space was not filled in, the PTFE will allow the new pipe to move more freely within the existing pipe during a seismic event.
PTFE is affixed to the area where segments of Bay Division No. 4 are sliplined.
Although the team did not identify any precedent on record for this technique, Steve P. Rados completed the sliplining without any issues and maintained a schedule of one 25-foot pipe segment per day. The existing pipe’s profile had minor inconsistencies, so prior to the start of slipline work the existing pipe was re-profiled with shotcrete that continued into the slipline pit. The new consistent profile on the existing pipe allowed for smoother welding fit up and eliminated any curbs or bumps the new pipe might have encountered while being pushed through the existing pipe.
The Seismic Upgrade of BDPL Nos. 3 & 4 benefits from the WSIP Safety Approach that the SFPUC has developed for all 80-plus projects in the program. The WSIP Safety Approach has achieved national recognition by industry and won the 2012 American Public Works Association Exceptional Performance Award in Safety. This programmatic plan for safety organizes and reconciles WSIP contract safety requirements, the California safety and health regulations and all applicable Federal and local regulatory standards. It also enshrines the goal of zero injuries on each project, establishes weekly presentations on safety topics and places safety responsibilities on the shoulders of the general contractor, the construction management firm and the program manager alike.
The Seismic Upgrade of BDPL Nos. 3 & 4 project is approaching 40,000 construction contractor hours without major or recordable accidents or incidents. Steve P. Rados shares the SFPUC’s priority for safety – their corporate values include promoting “a safety culture above all else.”
Water to rely on
With the devastation of the infamous 1906 ‘Great’ Earthquake and the freeway-flattening Loma Prieta earthquake of 1989, Bay Area residents and business owners know that the next major earthquake isn’t a matter of “if” but “when.” Upon completion at the end of 2014, the Seismic Upgrade of BDPL Nos. 3 & 4 will represent a significant improvement in the reliability of the water system following an earthquake. The system will provide water for firefighting, hospitals and other critical public services immediately after an earthquake as well as ensure a safe drinking water supply to customers. A strong construction team has enabled the project to progress in the face of unusual challenges.
ABOUT THE AUTHORS:
Bryan Dessaure, PE, has been a project manager for the San Francisco Public Utilities Commission for over ten years, and currently manages projects including the Seismic Upgrade of Bay Division Pipelines Nos. 3 & 4, Bay Division Pipelines Nos. 3 & 4 Crossovers Facilities, Geary Road Bridge Replacement, Millbrae Yard Improvements, Sunol Yard Improvements and Southern Skyline Blvd. Ridge Trail Extension. He has a bachelor’s degree in civil engineering from San Francisco State University.
John Prete is the construction manager for the Seismic Upgrade of Bay Division Pipelines Nos. 3 & 4 project. He has worked for the San Francisco Public Utilities Commission for more than seven years. Previously, he was an engineer for Caltrans. John has a bachelor’s degree in civil engineering from UC Davis.