How the earth underground resists missile attack

Hit hard by a missiles or meteor, materials like soil and sand actually get stronger to resist the force from penetrating deeper underground, says new research.

The findings help explain why attempts to make ground-penetrating missiles go deeper by simply shooting them harder and faster have had limited success, the researchers noted.

"Imagine you are trying to push your way through a crowded room," said study co-author Abram Clark, currently a post-doctoral researcher in mechanical engineering at Yale University in the US.

"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 are going to end up applying a lot of pressure and ramming into a lot of angry people," Clark noted.

The process is somewhat similar underground when the earth is hit hard by a missile or meteor.

For the study, the researchers developed techniques that enabled them to simulate high-speed impacts in artificial soil and sand in the laboratory, and then watch what happens underground close-up, in super slow motion.

They found that materials like soil and sand actually get stronger when they are struck harder.

Funded by the US Defense Threat Reduction Agency, the research may ultimately lead to better control of earth-penetrating missiles designed to destroy deeply buried targets such as enemy bunkers or stockpiles of underground weapons.

The study appeared in the journal Physical Review Letters.