Just beneath the topsoil, says Sibel Pamukcu, the layer of the earth’s surface known as the subsurface, or subsoil, plays a vital but poorly understood role in the health of society’s civil infrastructure.
As the topsoil sustains the earth’s rich tapestry of plant life, the subsurface provides the foundation for buildings, bridges and roads; for tunnels, pipelines and embankments — in short, for every manmade structure placed in or on the ground.
Pamukcu, professor of geotechnical engineering, leads an interdisciplinary team of researchers attempting to shed light on the densely packed clay and sand that make up the subsurface.
The group is developing networks of wireless sensors and installing them in strategic locations underground to monitor pipeline leaks, mudslides, pavement cracks and other “geo-events” that affect the performance of the infrastructure.
“The health of the civil infrastructure depends on events in the subsurface,” says Pamukcu, who works with Liang Cheng, associate professor of computer science and engineering, and Muhannad Suleiman, assistant professor of geotechnical engineering.
“We can see structures above the ground. We can examine a bridge and look for signs of deterioration. But we can’t see the subsurface or the hidden infrastructure of tunnels, embankments, levees, and bridge and highway foundations.
“Often this infrastructure is not monitored until a catastrophe occurs. So sensors have to be our remote eyes.”
In a project funded by NSF, Pamukcu, Cheng and Suleiman load transceivers, or breadboards, with sensors that are programmed to detect moisture, heat, soil movement, electrical conductivity and other characteristics of the subsurface. Changes in these characteristics, says Pamukcu, alter the way the transceivers transmit electromagnetic waves.
“We are trying to determine whether changes in the transmission of the electromagnetic waves are occurring because of the presence of liquid in the soil or because of compaction or loosening of the soil. These phenomena can be early warning signs of contaminant intrusion, the onset of a progressive slide or other events that normally appear to happen suddenly.
“Our goal is to be able to pinpoint the location of a likely event and to take precautions or preventive measures — to do forensic work — before the event occurs.”
Subsurface wireless sensor networks are not yet used to monitor the hidden infrastructure, says Pamukcu. She and her collaborators and their graduate students have installed and tested networks of transceivers in the soil on Lehigh’s campus and are building a room-size soil box in a laboratory. their aim is to learn how the electromagnetic wave signal is affected by the distance between transceivers and by the depth at which the transceivers are placed in the soil.
“We have been able to place our transceivers six feet underground and still get good transmission,” says Pamukcu. “We have also been able to show clearly in the lab that the transmission rate and signal both change drastically during a geo-event. And our system can identify and detect the location of injected fluid.
“The transceivers transmit well over short distances. Now we need to increase the distance of transmission and the battery life of the sensors. We need to stretch the envelope.”
Pamukcu’s group is developing mathematical models and comparing their results with data from physical experiments. The next step is to install a wireless network of transceivers in a new structure or in an existing structure that is being rebuilt.
“Our goal is to provide long-term monitoring options for a structure, its subsurface and its vicinity as well,” says Pamukcu. “This will be an online system.”