35 DECEMBER 2021 WorldWide Drilling Resource® RENEW - SUBSCRIBE NOW! Oregon State University Helps Port of Portland Prepare for a Megathrust Earthquake Adapted from Information by Oregon State University Oregon State University (OSU) College of Engineering provided blasting research to help the Port of Portland save up to $50 million on work to ensure a Portland International Airport runway can survive an expected magnitude 8.0 to 9.0 Cascadia subduction zone earthquake. The project was led by Armin Stuedlein, professor of civil and construction engineering, and involved three days of test detonations at the airport in 40- and 90-foot-deep blast casings. Studying the series of controlled blasts helped researchers determine how sand and silt soils underlying the airport would respond to a “megathrust earthquake” and what ground improvements are needed to prevent liquefaction and keep the runway intact. “The port needs to change the composition of the soils so they don’t turn into viscous liquids,” said Stuedlein. “It’s a very large area, and every part of the area that they don’t need to improve, because they understand the soils, will save millions of dollars.” The Port of Portland is a member of the Cascadia Lifelines Program, or CLiP, which OSU formed to conduct research to help Oregon’s largest infrastructure operators - such as the port, NW Natural, Portland General Electric, the Bonneville Power Administration, and the Oregon Department of Transportation - mitigate earthquake damage in the most effective and costefficient ways. “We put in $350,000 for Armin’s work to save $50 million or right around there,” said Tom Wharton, project engineer for the Port of Portland. “It was a no-brainer.” CLiP Director and Engineering Professor Michael Olsen described the program as a “powerful forum” bringing together lifeline service providers to address specific challenges associated with Cascadia subduction zone earthquakes. Cascadia quakes are fundamentally different than the ones California experiences, and also longer - 90 seconds or more, compared to 10 to 30 seconds. The airport project grew out of a 2016 resilience workshop CLiP hosted for its member agencies, which also included the Eugene Water and Electric Board, Portland Water Bureau, and the Tualatin Valley Water District. At the workshop, Stuedlein suggested blast testing to “excite the soils” to better understand how the airport ground would behave during a devastating quake. “When a big Cascadia earthquake hits, the Port of Portland is really the only possible venue to fly in supplies,” explained Stuedlein. “Having a runway serviceable is a key requirement for the whole Northwest; we expect I-5 to be shut down and bridges on the Columbia and Willamette to be out of service. Much of Oregon’s infrastructure was built long before seismic risk was fully understood.” Situated on 700 acres in northeast Portland, Portland International Airport has two main runways, each in a northwestsoutheast alignment. One is north of the terminal, along the Columbia River, and the other is south of the terminal. The 11,000-foot south runway, surfaced in concrete and more than 1000 feet longer than the asphalt-surfaced north runway, is the one the Port of Portland aims to keep open after a huge quake. “Both runways are close to the river and susceptible to earthquake-induced liquefaction,” said Stuedlein. “There’s 100 feet of liquefiable soil beneath the runways, and liquefaction is not as well understood at depths like that.” Wi th f inancial suppor t f rom the Cascadia Lifelines Project and National Science Foundation, as well as the Port of Portland, onsite work began in March 2018. Blasting, which followed the drilling of boreholes and the installation of instruments, occurred on three consecutive days in October 2018. “We just took the energy to the soil and created seismic energy similar to an earthquake,” said Stuedlein. “Before our work, no one had observed what we had observed, the way we observed it. And we showed that trends of liquefaction that had only been observed in the lab held true in the field - so we demonstrated that our experimental technique is valid for getting information that’s highly useful in understanding quake risk.” According to Stuedlein, the reason no one tried the technique before was EXB Oregon State University continued on page 36
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