Detecting and Protecting Tunnels
(December 2007) There’s a whole underground culture working for Department of Homeland Security (DHS). Scientists and engineers from different countries are peering and roaming about underground—that’s, literally, underground—to examine tunnels. In short, they’re trying to detect tunnels that shouldn’t be there … and protect the ones that should.
With funding from the DHS Science and Technology Directorate (S&T), researchers are tracking how seismic waves caused by vibrations travel through various layers of soil. By analyzing the movement of these waves (sometimes called rays), experts may be able to detect the presence of tunnels that are dug illegally along the U.S. border, usually by smugglers and possibly by terrorists.
Other researchers are examining the structure of large tunnels, such as railroad and highway tunnels that are crucial to everyday life. They’re trying to design a system that can automatically deploy giant air bags if a tunnel starts to collapse or sustains a gaping blast hole. These air bags would be made of some kind of heavy-duty, but inflatable, material that would temporarily seal breaks in the tunnel. They could allow just enough time for people to evacuate.
Both projects are part of a series of research grants issued recently by the S&T Directorate’s International Programs. The grants are given to teams of U.S. and foreign universities that are partnering on homeland security research.
The tunnel detection work is led by the University of Mississippi and the University of Alberta in Canada. Craig Hickey, a professor of geological engineering and physics at UMiss, directs the project. Basically, he bangs a hammer onto a line of sensors called geophones, which are placed strategically aboveground. Then, he uses a receiver hooked to a seismograph to track the resulting seismic waves as they travel through the ground.
“We’re measuring the timing and propagation of the waves,” says Hickey. “We’re looking at the velocity and path of each.” The technique, he says, is similar to ultrasonic imaging that is used in hospitals to make a medical diagnosis.
If a tunnel is underneath where Hickey and his team are working, they can usually note that the wave will travel in an unusual kind of way. The wave may quickly refract, for instance, back up to the receiver. “A tunnel affects the density and the elasticity of the ground around it,” he says.
Once all of the measured waves are recorded, Hickey charts them on a computer through a process called seismic refraction tomography. Hickey can often see abnormalities in the chart where a tunnel is located, sometimes with startling precision.
If Hickey’s method can be applied on a large scale, it could be a handy tool for border agents and law enforcement agencies. He says it may even be used to test the strength of levees, by looking at the density of the ground underneath them.
The tunnel protection work, meanwhile, is a collaborative effort between West Virginia University (WVU) and Lindstrand Technologies, based in the United Kingdom. Lindstrand manufactures air balloons and other inflatable structures. It has a prototype “tunnel plug” that could be used, if a fire breaks out, to seal off the openings of the tunnel, and thereby deprive the fire of the oxygen that it needs to burn.
Julio Davalos, a professor of structural engineering at WVU, is trying to take the tunnel plug idea to the next step—envisioning it as a way to actually seal breaks in tunnels or hold back the pressure from a break. More research is needed, and it’s still unclear what kind of material or “reinforced fabric” would be used, says Davalos. But the concept works like this: If a tunnel fails or bursts, sensors would activate a system—likely attached to the ceiling—that would deploy huge air bags on both sides of the breach to hold back debris or water. “We’re probably looking at anywhere from a few minutes to over an hour, depending on the significance of the event,” he says.
His first challenge, though, is to develop the deployable system itself. How would it be designed and installed? What type of sensors would trigger it to deploy? What exactly would it be sensing—a change in pressure, flooding, fire and smoke, or combinations of these parameters? All of these questions would need to be answered. “An intelligent system would be needed, along with a decision-making protocol,” adds Davalos. No doubt, an ambitious project, he says, but researchers hope to have a working model within three years.
“We’re excited about these efforts,” says Paul Ragsdale, a science advisor with International Programs. “For the first time, we’re tapping S&T capabilities around the world to solve some of our biggest domestic security challenges.”
In addition to the tunnel projects, International Programs has provided a grant to the Massachusetts Institute of Technology to work with the Mexican Navy, studying how acoustic sensors can be used to determine the intensity of hurricanes. The National Center for Food Protection and Defense (NCFPD), based at the University of Minnesota, has also received a grant. NCFPD will organize a large-scale, international training exercise to prepare for the possibility of a global outbreak of contaminated food.
International Programs has also begun accepting applications for a second round of grants, to be announced in 2008. Details are available at www.grants.gov.