Averting that sinking feeling
In a Magnitude 9.0 Cascadia earthquake, which is long overdue in western Oregon, one of the big fears is that the damp soil on the banks of the Willamette and Columbia rivers will liquefy and send homes and businesses tumbling.
Worst of all, the land under chemical tanks along U.S. Highway 30 in Northwest Portland could shake them off their concrete pads and split them open to create a toxic stew of gas and sludge.
Arizona State University has developed technology for mitigating liquefication that involves injecting nutrients down pipes into the soil. Micro-organisms feast on the nutrients and produce tiny bubbles of gas. These act like Styrofoam packing peanuts and prevent the pressure build-up that turns wet soil into a mobile soup.
According to a Portland City Club report, 90% of Oregon's liquid fuel supply is kept in fuel tanks in the Critical Energy Infrastructure (CEI) hub in Northwest Portland. Those fuel tanks are sitting on the before-mentioned unstable soils.
An ongoing Portland State University study is testing the new microorganism treatment at two sites in Portland. The study is funded by the National Science Foundation and includes collaborators from Oregon Department of Geology and Mineral Industries, Arizona State University and the University of Texas at Austin. The first site is a 62-acre habitat restoration area owned by Portland General Electric in Northwest Portland, known as Harborton. The study says the similarities of the soils at Harborton to the soils under the fuel tanks in the CEI hub provides an opportunity to test if the new treatment will provide a viable solution for one of Oregon's serious resiliency concerns in the aftermath of a significant earthquake.
The second site is a recycling site called Sunderland owned by Portland Bureau of Transportation, where PSU recently put on a demo. It is near the Portland International Airport and 100 yards from Dignity Village.
University of Texas at Austin professor Ken Stokoe and his team demonstrated a machine that simulates an earthquake. The 64,000-pound mobile shaker is called T-Rex. It is a truck with a large metal disc attached to its underside. When T-Rex lowers the disc, it shivers and shakes to cause resonant frequencies in the soil below it. During a demonstration, when the T-Rex disc was finally turned on, it made a noise, and the grass shivered. A minute later, it was turned off.
The demonstration did not show much to the layperson, but during three hours of talking, scientists and academics made two things clear: Portland has a liquefication problem, and the new treatment could be an affordable way to fix it.
Since 2008, when a tall building is built in Portland, the code states that the foundations must reach down below the liquefiable layer. The cost of digging below the foundations of the Burnside Bridge or some of the older brick buildings in downtown Portland is unthinkable. However, with this technique, it could be cost-effective to drill wells and feed the micro-organisms and have the bugs create the gas (nitrogen). The wells would be capped and tested every few years to see if the gas was still at the right levels.
PSU could save Portland
Arash Khosravifar and Diane Moug, assistant professors in the civil and environmental engineering department at Portland State University, are conducting the study with their graduate students. Khosravifar explained, "Liquefication is triggered when the weight of soil grains is canceled out by the buoyant force from the high pressure from the fluid. And that only happens if the soil is fully saturated. If you manage to reduce the saturation percentage below the water table, you don't trigger liquefication.
"What we wanted to showcase today is a new advancement in liquefication mitigation that was developed by researchers at Arizona State University," Khosravifar said. "They've been working on it for a couple of decades, and now we've got to a point where we can apply it in the field to determine if it can be an effective choice to mitigate the liquefaction risk for Portland soils."
If it works, it can be done to existing structures.
"That would really be a game-changer because you can mitigate liquefication at a fraction of a cost compared to existing methods," Khosravifar said.
Edward Kavazanjian, professor at Arizona State University, said this is the first field-scale application of this technology for saturated soils.
"We've done a lot of laboratory work. We had a similar project in Toronto with slightly different goals."
Asked how far away from being a viable commercial product that cities and ground improvement contractors can buy and use, Kavazanjian said, "A couple of years, there's still work that needs to be done. But this will provide a demonstration that it works under relatively adverse conditions. The soils here are perhaps not the most amenable to this kind of treatment because it's fine grain, and there's an interlayer of sands and silts. If we have clean strata, it'll work like a charm. But when you get the soils like silts, it's harder for the nutrients and the gas to penetrate the soil."
A local ground improvement contractor named Condon and Johnson provided help on the installation of the wells and the pumping system. "On their own dime because they realized the potential for the work."
Cross your fingers, Portland
One issue is how do they verify to a regulatory agency or an owner that it's working? It's a wait-and-see process.
Kavazanjian said, "It's a combination of the technology being ready, and the market being ready when there's a critical need. I think there is a real critical need for liquefication mitigation under existing structures, like in your critical energy infrastructure hub, that can accelerate the pace of which is adopted. There's really nothing else you can do there, except cross your fingers and hope the earthquake doesn't come back."
How scared should Portlanders in small wooden homes be?
"This wasn't in the building code until 2006," Kavazanjian said, "and even now, it exempts single-family homes. A small earthquake in Christchurch, New Zealand, in 2011, a magnitude 6.3, — well below the level of shaking you expect here — that damaged 15,000 modern single-family homes beyond repair."
The damage to structures and infrastructure was estimated at $10 billion to $15 billion.
"They could have done it in New Zealand in advance. It's the kind of thing where a drill rig comes up, and we put some wells in the ground. To remediate 15,000 homes would be a big challenge. It would take a decade or more."
Kavazanjian said there is data from Japan and from laboratory testing in the U.S., that suggests that the treatment will persist for decades. "But it needs to be monitored. If 10 or 15 years from now the gas started to dissipate, we would just feed some more nutrients."
Khosravifar said the lack of urgency about preparing for an earthquake in Oregon doesn't frustrate him.
"But it's something that we have to do. The recent scientific discoveries indicate that a large magnitude earthquake is waiting to happen like a ticking bomb. Liquefication mitigation techniques are expensive, and doing seismic upgrades to our structures is expensive," Khosravifar said. "As Oregonians, we have to decide how we want to spend our resources. Do we want to spend it on schools, fix the roads, or solve the housing problems? Or, do we want to spend it on liquefaction mitigation and reducing the risks of a catastrophe waiting to happen at the CEI hub? The price tag is huge. And hopefully, this new treatment, if proved effective, reduces the costs."
What about the building that Khosravifar works at Portland State University, a five-story building called the Fariborz Maseeh College of Engineering and Computer Science?
"That's a new building, built to code and sitting on pretty good soil," he said.
He feels safe.
Reporter, The Business Tribune
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