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A new Portland State University study asks: how will structures with pile foundations fare when the soil turns to liquid?
Author: Shaun McGillis, Research & Graduate Studies
Posted: August 15, 2018
The 9-meter geotechnical centrifuge at the University of California, Davis--part of the NSF Natural Hazards Engineering Research Infrastructure--can simulate the high pressures found deep in the ground within small-scale models while hydraulic actuators sThe City of Portland’s Bureau of Emergency Management has a map identifying areas of the city considered susceptible to liquefaction in the event of major seismic activity like what might be expected during a Cascadia Subduction Zone earthquake. The good news is, the vast majority of the city’s neighborhoods and commercial districts are on solid ground. The bad news is, liquefaction could cause serious damage to critical infrastructure including the airport and port terminals, the majority of the city’s bridges, the power grid, and the “tank farms” in Northwest Portland where fuel reserves are stored.
 

Soil liquefaction is a phenomenon that occurs when a force, such as the shaking during an earthquake, causes saturated, low-density soils to lose their strength and rigidity. Once liquefied, gravity pulls the soil down slope. The resulting lateral spreading can wreak havoc on surface structures and infrastructure.

For centuries, structural engineers have designed buildings and structures with deep foundations on sites with low-density soils. Pile foundations (a type deep foundation) are those in which piles are driven through unsuitable soil and embedded in more competent rock formations.

Despite decades of research examining how pile foundations respond to forces associated with earthquakes, there are still gaps in our understanding of how these foundations and the structures they support perform under liquefaction conditions.

Dr. Arash Khosravifar, an assistant professor of geotechnical engineering at Portland State University’s Maseeh College of Engineering and Computer Science, conducts research that seeks to improve understanding of how pile foundations behave under soil liquefaction conditions. Khosravifar recently received a $100,000 grant from the National Science Foundation to study how structural load demands and lateral spreading resulting from soil liquefaction combine during long-duration, high-intensity earthquakes like those that occur along subduction zones.

Using simulated earthquake data generated by Oregon State University researchers at UC Davis’s Center for Geotechnical Modeling in combination with numerical and computer modeling, Khosravifar will explore the factors that affect structural loading and liquefaction-induced lateral spreading.

“This is an area of research where there are still questions that need to be answered,” Khosravifar said. “This study will look broadly at the effects of liquefaction on piles for wharves and ports using data from centrifuge tests conducted by my collaborators at Oregon State. The narrow objective, and the question we’re trying to answer through this study, is how these two forces, the structural load from the wharf and the lateral spreading of liquefied soil interact in relation to piles during long-duration earthquakes.”

According to Khosravifar, addressing this knowledge gap could lead to improvements in design codes in regions prone to seismic events like the Pacific Northwest, Japan, and Chile. Those improvements, in turn, could result increased public safety by enhancing structural resiliency for buildings and infrastructure in areas that may be susceptible to soil liquefaction.

Image: The 9-meter geotechnical centrifuge at the University of California, Davis--part of the NSF Natural Hazards Engineering Research Infrastructure--can simulate the high pressures found deep in the ground within small-scale models while hydraulic actuators simulate earthquakes. Hundreds of sensors measure the response of the soil and model structures. Image credit: Center for Geotechnical Modeling, UC Davis.