Study examines underground effects of missiles, meteors

DURHAM, N.C., April 10 (UPI) -- What happens to the subsurface soil and sand impacted by missile or meteor? It's not an everyday question, but it's one that intrigued scientists at Duke University, so a group of physicists there decided to find out.

Neither waiting for a meteor impact nor shooting real missiles at the ground were viable options, so the scientists simulated high-intensity impacts in the lab using artificial sand and soil. To mimic the impact, researchers dropped a bullet-like pointed metal ball from seven feet above.

Researchers were able to observe the effect of the impact by using clear plastic spheres that transmit light when compressed. Slow-motion imaging showed the lightening-like paths of light created as the faux sand molecules compressed against each other.

The chain-reaction of light showed that low-intensity impacts had rather shallow effects, where as high-energy impacts created compression chains penetrating deep into the soil. The harder the impact the more intense the compression -- or what the researchers called "nonlinear force propagation." The more intense the compression, the stronger the soil became.

"Imagine you're trying to push your way through a crowded room," study co-author Abram Clark, a postdoctoral researcher in mechanical engineering at Yale University, explained in a press release. "If you try to run and push your way through the room faster than the people can rearrange to get out of the way, you're going to end up applying a lot of pressure and ramming into a lot of angry people."

Researchers say the study -- published this week in the journal Physical Review Letters -- could help military engineers better protect underground structures from bunker-busting missiles.