Digging Deep

In the summer of 2019, Kayla Sorenson '19 '21, now a Ph.D. candidate in civil and environmental engineering at Portland State University, spent every day working as a student intern at research sites just west of the airport and along the Willamette River. Her days started at 7 a.m. when she began taking seismic measurements for an important team that was researching how to make soils more stable during earthquakes.

The days were long and hot, but Sorenson didn't care. She was happy to be in the field and away from her desk. She was also compelled by the project, which she knew could help better prepare the region for the prospect of the big Cascadia quake.

"She was there every day with a great attitude, helping us to troubleshoot and problem solve and get things going," says Diane Moug, assistant professor of civil and environmental engineering at PSU. "Regardless of the weather, regardless of what hiccups we ran into, she was there."

During her internship, Sorenson became fascinated with the research, and this fascination led her to a long and decorated academic journey at PSU, first earning a master's degree before pursuing her doctorate.

Sorenson's dedication to her research has made her a key collaborator on the research team, and an academic all-star. She was recently awarded fellowships from the U.S. Department of Transportation and the Federal Emergency Management Agency (FEMA)/Earthquake Engineering Research Institute (EERI).

The EERI/FEMA fellowship recognizes graduate students who show a strong promise to advance the field of earthquake risk mitigation, and is only awarded to one student each year.

"I've been on the committees that decide on those scholarships, and it's very competitive," says Arash Khosravifar, PSU associate professor of civil and environmental engineering.

She was also compelled by the project, which she knew could help better prepare the region for the prospect of the big Cascadia quake.

A rocky start

While Sorenson has earned many accolades during her time at PSU, her academic journey hasn't always been smooth.

After graduating from high school in 2009, she headed to Oregon State University, where she started studying mechanical engineering before switching to construction engineering management. She liked the field but struggled with the transition to college.

"I really didn't have any issues in high school," says Sorenson. "I didn't have to study, which kind of set me up for failure." Eventually, her grades dropped, and she decided to drop out.

She moved back to Portland to live with family and pay off her student loans. She still wanted to get a bachelor's degree but knew that time and costs were going to make that difficult.

Sorenson started taking engineering classes at Portland Community College, one course a term. In 2017, she transferred to Portland State to finish her degree in civil engineering, which was the closest degree that fit the credits she'd already earned.

Initially, Sorenson picked PSU because it was the easiest university to commute to. She quickly learned that it offered her much more. "It wasn't until after I started taking classes that I really started to understand the quality and caliber of the research that is being performed [at PSU]," she says.

Sorenson found her stride. She took courses that she loved, connected with faculty mentors, got her hands dirty with field work and became engaged in outreach work.

Summer of soil

As an undergraduate student in PSU's civil and environmental engineering department, Sorenson discovered a passion for geotechnical engineering - the engineering of soil and dirt.

She sees parallels between her interest in geotechnical engineering and her experience in technical theater in high school. Both involve working behind the scenes and setting the stage. "With geotechnical engineering, I found something that let me get on a project before the ground floor was even built," she says.

Her interest in the field showed through in her courses. She excelled and caught the eye of Khosravifar, who hired Sorenson to work on the research team in 2019.

Sorenson joined the team as a summer intern as part of PSU's Research Experience for Undergraduates (REU) program. This program supports students working on research funded by the National Science Foundation (NSF).

Sorenson's REU project was part of a large NSF-sponsored collaboration between PSU, Arizona State University and the University of Texas at Austin to test a new method for preventing liquefaction caused by earthquakes.

To understand liquefaction, says Sorenson, think of those cheesy movies from the 70s and 80s where people were constantly sinking into quicksand. "The ground turns into soup," she says.

When liquefaction occurs following an earthquake, buildings, communication towers and roadways can all sink. "Pretty much anything on top of the surface, it's going to get affected by it," says Sorenson.

This is a big problem for Portland and its infrastructure when considering the potential of the Cascadia earthquake, the large earthquake that scientists say has a 37% chance of hitting the Northwest in the next 50 years. In Sorenson's mind, we are not adequately prepared.

While we now know that liquefaction is a hazard, we didn't really understand the risks of a Cascadia earthquake until the mid-1990s. Structures built before the 90s were built without the appropriate codes for earthquake safety that we use today.

"If you look at all the massive earthquakes that Japan has had recently, they know about this threat, and they are prepared for it, and they still had huge damages and unbelievable loss of life," says Sorenson. "We are not. We are aware of this risk. We are working toward getting resilient, but we haven't really done the huge steps that need to be taken."

What can we do to better prepare for the "Big One?" That's the question that has guided Sorenson's research and outreach work at PSU.

Burping bacteria

During her internship, Sorenson tested an innovative method for preventing liquefaction during earthquakes by strengthening the soil. The method involves pumping nutrients into the ground to feed microbes underground. These well-fed microbes then release tiny bubbles of carbon dioxide and nitrogen gas. "They'll basically burp," says Moug.

The microbe burps are key to strengthening the soil. "These tiny bubbles are going to act as basically an air cushion," says Sorenson.

This technique, which is known technically as microbially-induced desaturation, was developed at ASU's Center for Bio-mediated and Bio-inspired Geotechnics. Sorenson was part of the first team to test it in the field.

The PSU team tested the technique at two different sites: a site just west of Portland International Airport (named the Sunderland site) and a site at the north end of the Critical Energy Infrastructure (CEI) hub along the Willamette River.

The CEI hub is of particular interest when it comes to earthquake risk. It's home to more than 90% of the state's liquid fuels and most of their tanks were built on liquefiable soil. If a large earthquake occurs, these tanks could end up settling, tilting or deforming. Any damage could cause fuels to spill into the river and could even cause fires.

"Not only is there the environmental concern, which is significant, we're going to need that fuel to recover following the earthquake," says Moug. "I think almost all of the jet fuel for the airport passes through the CEI hub. If we don't have that fuel to move people and goods in and out of the airport, we can't recover as quickly."

At both sites, the research team fed nutrients to the microbes through an input well dug six to 20 feet into the soil. But they had doubts about whether the bubbles would be able to form at all in the fine grained silty soils at the sites.

"We thought it would be kind of a high risk, high return type of research," Khosravifar says.

Sorenson's job was to take seismic measurements every morning to see whether the technique was working. About 14 days into the treatment period, she started getting sensor data showing that the gas bubbles were being created. The technique was working as they hoped, much to everyone's excitement.

"It wasn't easy research, but it paid off, and it has really opened a door for a lot of other research," says Khosravifar. In fact, it's paid off literally. Moug and Khosravifar received more than half of a $1 million dollar research grant last year based on the success of the team's pilot project.

For her part, Sorenson has stayed actively involved in follow-up research while earning her master's degree and working towards her doctorate.

Dirt dissertation

Sorenson collecting data from the Sunderland site

For part of her graduate work, Sorenson has continued to visit the Sunderland site to see how long the microbe treatment lasts. "No matter what the condition of the field site is like, if it's pouring rain and it's flooded, she's out there getting data," says Moug.

Sorenson has discovered that the gas bubbles are still there - almost five years after the treatment and despite annual floods at the site, much to the team's surprise and happiness.

"If this method is going to eventually be used in practice, we need to be able to show that they're persistent and we need to show the longevity of this method, and Kayla's research basically shows that," says Khosravifar.

For her dissertation research, Sorenson is trying to nail down the target level of microbially induced desaturation that is ideal for strengthening soil before an earthquake arrives.

To probe this question, Sorenson places soil specimens about the size of a hockey puck with different levels of saturation into a machine that can simulate earthquake shaking. She then adds weights to the soil to see whether they will sink during the shaking, a process that tests the strength of the soil.

She's currently testing the apparatus on sand but will next test silt and clay and, eventually, soil samples from the CEI and Sunderland sites.

"Ideally we would be able to see the differences in how much desaturation needs to happen in each type of soil," says Sorenson. "And then we can correlate that to real world conditions."

Preparing Portland

Sorenson's work on microbially induced soil desaturation may one day help Portland prepare for earthquakes. Current techniques for preventing liquefaction-like inserting blobs of concrete underneath buildings-are expensive and often require digging up sidewalks or closing down buildings.

In contrast, microbially induced desaturation would likely be more affordable and relatively non-invasive. "Yes, you would have some machinery out there, but it would be like three days versus a week of loud construction," says Sorenson.

If the technique ends up being viable, the research team's Portland connections could help hasten its adoption. The researchers already have strong relationships with Portland General Electric and the Portland Bureau of Transportation, partners at the CEI and Sunderland sites, respectively, as well as with Portland engineering companies.

"We're located in downtown Portland," says Moug. "They can see our work and meet our students, and provide feedback." Already, local companies and major Portland area infrastructure projects send soil samples to the lab for testing to see how the soil would fare in an earthquake.

We're invested in this work because we see that it's important to our communities and the city that we have a seismically resilient city, area and state.

"We're invested in this work because we see that it's important to our communities and the city that we have a seismically resilient city, area and state," says Moug. "We can be prepared and we can be a model for earthquake preparation, both in terms of infrastructure and personal preparation. I really hope that we become a success story of getting through the earthquake."

Future Forward

Throughout her time at PSU, Sorenson has spread the word about earthquake preparedness through outreach activities and teaching. "It's been really phenomenal to see how dedicated she is and how involved she is," says Khosravifar.

Sorenson has worked with the City of Portland Bureau of Emergency Management to hold a large outreach event about updating laws and codes for emergency preparedness, led research demonstrations, mentored undergraduate students and served as a teaching assistant for several engineering courses.

Since 2020, she's also served on the Earthquake Engineering Research Institute (EERI)'s Student Leadership Council. Last year, she served as co-president to lead planning and judge a seismic design competition for undergraduates across the world.

"It's one of the most difficult roles in the competition because you're interacting with all these students who put their heart and soul into a project and are very invested in their results," says Maggie Ortiz-Milan, Director of Programs at EERI. "There's a lot of pressure to make sure you're being fair, that you're being transparent and that the results are accurate. Having seen Kayla come through that is pretty impressive."

After earning her Ph.D., Sorenson plans to continue working with others in the name of earthquake preparedness, and hopes to combine her research knowledge with her collaboration skills in her future career.

"I would love to be tied into ongoing research at all universities and help coordinate these pieces to make earthquake preparedness and resilience better," she says.

Sorenson is proud of her outreach work and research, as well as how far she's come in her time at PSU.

"It took me 10 years to get my bachelor's degree after I failed out of Oregon State. Now I'm here for my Ph.D., which I never, ever thought [was possible]," she says. "The research, it's captivating, which is why I've stayed around."

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