Collaborative study led by Portland State University uses T-Rex machine to simulate earthquakes as part of study to mitigate soil liquefaction
Author: Katy Swordfisk, PSU Media & PR
Posted: September 13, 2019

Portland has a liquefaction problem. The soil, thanks to the city’s proximity to the Columbia and Willamette rivers, is susceptible to liquefying during a large earthquake — such as a potential Cascadia quake — and is expected to cause widespread damage.

 “It is important to mitigate liquefaction to improve the resiliency of the state of Oregon in the aftermath of a major earthquake,” said Arash Khosravifar, Portland State University civil and environmental engineering professor in the Maseeh College of Engineering & Computer Science.

Khosravifar and his team are looking for a solution to prevent soil from liquefying. Their study is funded by the National Science Foundation (NSF). Existing methods are expensive and often cannot be applied to existing infrastructure, such as fuel tanks and underground utilities. 

“We’re working on an innovative method that uses one of the new advancements in the field of liquefaction mitigation,” Khosravifar said.

The method, called bioremediation, uses the existing microorganisms in the soil to reduce the soil’s moisture content and mitigate potential liquefaction. The method was developed by researchers at Arizona State University’s Center for Bio-mediated and Bio-inspired Geotechnics and PSU is applying it in the field at two locations in Portland.

Khosravifar's team began applying the treatment in July at two test sites, Harborton Substation and Sunderland Yard. Harborton is a 62-acre habitat restoration project owned by Portland General Electric in Northwest Portland. It’s located within the Critical Energy Infrastructure (CEI) hub — where 90% of Oregon’s liquid fuel and all jet fuels for Portland’s airport are handled. Without fixing the soil, the tanks in the CEI hub could rupture not only causing a widespread fuel shortage, but spill oil into the Willamette River triggering an environmental disaster of epic proportions.

Sunderland is a city-owned site in Northeast Portland near the Columbia River in the city’s industrial area.

“PGE is proud to support this important effort by offering our Harborton property as one of the study sites,” said Chris Bozzini, senior manager in PGE’s Environmental Services Department. “We recognize the study’s potential for improving community resiliency in the face of an emergency — something our company values tremendously.”

Diane Moug, PSU assistant professor, said they are treating similar soils that are under the fuel tanks in the CEI hub and the airport runways.

“Not having our airport function will be devastating to the recovery of Portland and Oregon following the earthquake,” Moug said. “Finding a way to mitigate these soils that underlie the airport and other critical infrastructure in Portland in a cost-effective way is going to be really beneficial to Oregon and our resilience in an earthquake.”

The next step is to simulate an earthquake on the sites and see how the soil holds up. To do so, Portland State is working with University of Texas at Austin. Professor Ken Stokoe and his team from UT have brought a large truck known as T-Rex to Portland. T-Rex is a mobile field shaker that will simulate an earthquake and measure changes in the soil to evaluate the effectiveness of the ground treatment. T-Rex is a part of an NSF-funded network of facilities called the Natural Hazards Engineering Research Infrastructure (NHERI) which enables researchers from
other institutes to use their equipment with reduced cost.

“If the method is proved to be effective, then it could be a game-changer,” Khosravifar said. 

After one month, testing showed that soil desaturation was already taking place.

“The method seems to be working,” he said.

Their plan is to monitor the sites for the next three to five years to see if the results are long-lasting.

“We’re very excited for the immediate results here, and for the long-term prospects for this technology to address this really critical need for mitigating liquefaction under existing facilities,” said ASU Professor Ed Kavazanjian, who also serves as director of CBBG and partner in the project.

The funding for this study was provided by the NSF through a RAPID grant, a fast-track mechanism, that made it possible to conduct the study this summer. This was due to the urgency to find a suitable ground improvement method at the CEI hub, as Oregon Seismic Safety Policy Advisory Commission was directed by the Governor’s State Resiliency Officer and Legislative member to address the CEI hub’s problems and provide a report in 2019. The project includes collaborators from Oregon Department of Geology and Mineral Industries, Arizona State University’s Center for Bio-mediated and Bio-inspired Geotechnics, University of Texas at Austin, Portland General Electric, Portland Bureau of Transportation and Portland Water Bureau, and industry partners including Condon and Johnson Associates and ConeTec.