by Mary Caperton Morton Tuesday, December 27, 2016
Southern California is notoriously dry, and the city of Los Angeles imports its water from Northern California. But there’s a potentially disastrous hurdle to cross: The San Andreas Fault runs just north of Los Angeles, slicing across all four of the major aqueducts that deliver water to the city. In the event of a major earthquake, water supplies to 4 million people could be cut altogether. The Los Angeles Department of Water and Power (LADWP) is working to disaster-proof the aqueducts as well as the 12,000 kilometers of pipelines that run throughout the city. A recent round of testing of a new type of earthquake-resilient pipeline at a specially designed laboratory at Cornell University is reassuring the LADWP that they’re on the right track.
In 2008, the Great Southern California ShakeOut earthquake exercise unleashed a simulated magnitude-7.8 earthquake on the San Andreas Fault just east of Los Angeles. One of the unforeseen consequences of the simulation was a fault rupture great enough to cut all four aqueducts at once. “That was something of a paradigm shift,” says Craig Davis, the water system resilience program manager at the LADWP. In response, the LADWP created a water supply task force charged with making the city’s water supply more resilient to earthquakes. Los Angeles mayor Eric Garcetti also announced the “Resilience by Design” plan with the goals of updating and fortifying the city’s physical, social and economic foundations in the event of a major earthquake.
“California has been very lucky, so far,” says Tom Jordan, director of the Southern California Earthquake Center (SCEC). “A number of smaller quakes have caused complications with the water systems, but those were relatively small events. The San Andreas Fault is capable of causing much more damage than we’ve had to deal with yet.”
The water supply task force is working closely with the U.S. Geological Survey and SCEC to map out the most potentially vulnerable areas of the city, Jordan says. “When you’re dealing with infrastructure distributed over such a wide area, you have to figure out how shaking might affect the system as a whole. We’re developing some new mapping tools that are really useful in assessing hazards to distributed systems, such as water, power and gas lines.”
Los Angeles boasts 12,000 kilometers of pipelines making up one of the largest and most complex water pipeline networks in the country. The pipes range in size from major transmission pipelines up to 3.5 meters in diameter down to distribution pipes as small as 5 centimeters, some of which are nearly a century old. “We are currently running an ongoing pipe replacement program that will never end,” Davis says. “A lot of our pipes are now reaching the end of their life span. As we replace them, we are replacing some of them strategically with seismic-resilient pipes.”
Japan has been tackling the problem of earthquake-proof pipelines for decades, and the latest technology Los Angeles is using is being manufactured by a Tokyo-based company, JFE Holdings. The company claims their uniquely designed pipes can withstand ground failure, fault ruptures, liquefaction and landslides. “This is the first type of pipe I’ve seen with these capabilities that is cost effective,” Davis says.
To test the JFE pipes, Davis traveled to the Geotechnical Lifelines Large-Scale Testing Facility at Cornell, a large-scale lab that can simulate the effects of earthquakes on sections of pipe. A team led by Thomas O’Rourke, an engineer at Cornell, buried an 8-meter-long section of 20-centimeter-diameter pipe under 80 tons of soil and used a hydraulically powered split box to displace the pipe by half a meter along a 50-degree crossing angle, compressing and bending the pipe to simulate the damage a ruptured fault could cause.
Any ordinary pipe would break under such circumstances, but the JFE pipe was equipped with two “wave features,” designed to bend and flex under strain, like the bendable neck of a drinking straw. “The pipeline far exceeded our expectations,” Davis says. “We moved it three times farther than what the manufacturer recommended and even then it didn’t rupture.”
The pipe shows huge promise in part because the wave features can be retrofitted onto existing pipelines, helping to keep replacement costs lower and minimize interruptions to water flow. “Being able to retrofit our existing system and improve the seismic-resilient network on both the transmission and distribution sides is both cost effective and low impact,” he says.
The LADWP plans to replace 8 kilometers of mainline pipes by 2020, prioritizing the most critical customers, such as hospitals, fire stations and emergency evacuation centers. “It’s quite an enormous task, but we’re figuring out how best to tackle it one piece at a time.”
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