We’ve all felt it as we drive along South Carolina’s roadways — the bumps, the ruts, the cracks.
South Carolina’s pavement designs, which date back to a method developed in the 1960s and 70s, are based on limited materials and performance data. Now, computer models can take into account how asphalt performs using a wide variety of factors, including climate conditions and traffic loads. But that new methodology relies on national data that must be collected from states around the country.
Enter Sarah Gassman, a civil engineering professor in the College of Engineering and Computing. Gassman has always been interested in structures built out of earth materials, soils and rocks.
“Everyone knows what pavement is. They don’t necessarily know the intricacies of the mechanics behind all of it,” she says. “That’s where I come in. “
For the past several years, Gassman has worked with Clemson University and the S.C. Department of Transportation on a $1.7 million study to better understand the pavement design needs in South Carolina.
“With a new model that takes into account all of these factors, each state in the U.S. needed to essentially calibrate the model for specific local conditions,” she says. “The materials that South Carolina uses for asphalt and pavement are different than, say, what are used in the West, where it’s an arid region and the sources of the materials are different.”
“Everyone knows what pavement is. They don’t necessarily know the intricacies of the mechanics behind all of it. That’s where I come in.”
Along with understanding the climate and the materials used to pave new roads, researchers also have to measure the stresses in the pavement.
“So, you have a pavement that’s newly constructed,” Gassman says. “Five years later, are there cracks? How is the pavement performing? What we do is collect all the materials, climate and traffic data. And we also collect the performance data, the rutting and the cracking, and we feed that data into the model and that will give us better predictions for how a pavement will perform.”
As part of its findings, the team was able to calibrate the model to predict the rideability — or smoothness — of the pavement. But she says more work needs to be done to predict cracking. Once there is cracking, the goal is to quickly remediate the pavement before big chunks start chipping off.
“People always ask about potholes, but those are a little bit different,” she says. “They can be caused by extensive cracking, but they’re also due to inadequately designed subgrade, which is the soil beneath the pavement. And sometimes that can cause erosion and lead to potholes in the pavement. That happens after winter when the pavement freezes and thaws.”
After a delay during COVID-19, the report was completed last fall. Data collected for roads across South Carolina will be input into the model to design future pavement.
A better bridge
By Chris Woodley
In August, USC civil engineering faculty members Juan Caicedo and Inthuorn Sasanakul began a four-year, $1.5 million project to rewrite the South Carolina Department of Transportation’s seismic design manual for bridges.
In addition to bridge design, the updated manual will provide current information pertaining to the structural components of bridges as well on soil and foundations relevant to geotechnical engineering.
“Instead of trying to develop new theories about earthquakes or new materials, we want to better understand earthquake engineering and the best practices for the state,” says Caicedo, chair of USC’s Department of Civil and Environmental Engineering.
But there are challenges for geotechnical earthquake engineering in South Carolina. One is the lack of moderate or significant earthquakes in the state. Unlike an earthquake-active state like California, this limits the amount of data available to understand dynamic loads.
Another issue is the varying geological features in each region. Deep and soft soil exists near the coast, which can cause soil liquefaction. The Midlands has more rock outcrops closer to the surface. The Upstate has a combination of rocks and mountains. More research and data are necessary for improving seismic design and to better understand how types of soil differ based on geological features.
“Instead of trying to develop new theories about earthquakes or new materials, we want to better understand earthquake engineering and the best practices for the state.”
“The different soil profile is important for seismic design,” says Sasanakul. “We need to know how the earthquake load is actually spreading in the ground and coming up to the surface.”
Sasanakul and her collaborators are now performing a range of tests at the College of Engineering and Computing’s geotechnical centrifuge facility.
“Before we assess whether the material will be affected or liquefy during an earthquake, we must perform an engineering characterization of dynamic soil properties. This testing measures the stiffness of the material to understand its strength,” Sasanakul says. “We are looking at the soil and a model of the structures because we’re interested in how the foundations interact with the soil.”