High-pressure air injections could aid contaminated soil cleanups

After shooting pressurized air into cells packed with sand and saturated water, scientists used advanced imaging technology to trace the intricate shapes created by the injections. The unique structures resemble tree branches or blood vessels.

"It is surprising to see that widely different systems can produce patterns that look eerily similar," Bjornar Sandnes, an associate professor of engineering at Swansea University, said in a news release. "Often this is because, deep under the surface, they share some mathematical guiding principle."

Though complex in appearance, analysis showed the compressed air simply follows different paths of least resistance. As the air pushes through the material, the sand becomes compressed around the edge of each branch, preventing other fractures from veering close by.

The research -- detailed in the journal Physical Review Applied -- could have a number of potential applications.

"We study these patterns first and foremost because we are curious to discover what physical mechanisms shape the form and function of these beautiful structures, but also because these processes are important in many natural and industrial systems," Sandnes said.

Scientists believe air fracturing could be used to improve the cleanup of contaminated soil sites. A strategy known as in-situ chemical oxidation is often used to detoxify land that's been contaminated by years of industrial use and pollution. A chemical is soaked into the sediment and allowed to react with the contaminant, rendering it harmless.

But not all sediments are easily penetrated or saturated. By injecting the land with pressurized air, the oxidant could travel throughout the contaminated soil through the branch-like fractures.

"By fracturing the soil, high-conductivity pathways can be generated for fluid exchange, speeding up the cleaning process, and reducing cost for the operator," researchers wrote.