Professors engage in ‘groundbreaking’ research

It’s hard to find Craig Benson and Tuncer Edil behind their desks. You would have a better chance of locating the civil and environmental engineering professors on a construction site, where they work, teach and learn about soil stabilization.

Benson and Edil are currently involved in two major projects that are resulting in environmentally safer and more cost-effective road construction.

They are testing the effect of fly ash on ground water at a road construction site in Cross Plains and helping the Department of Transportation create a more durable surface on Highway 60 near Lodi.

The newly paved roads in the Scenic Edge development in Cross Plains once were muddy pathways that made it difficult to move heavy construction machinery. The soil was very moist, so contractors needed to take extra measures to stabilize the soil under the new streets. Typically, this would require them to remove wet soil and replace it with crushed rock, a time-consuming, costly process.

In addition, both the removed soil and the replacement rock would be transported through city streets, potentially damaging them. With the help of Benson and Edil, contractors have found a much more cost-effective way to handle the problem.

The contractors mixed fly ash, a powdery material that is created when coal is burned for fuel, into the moist soil to form a stiff substance. Because fly ash is a waste product that might be sent to landfills if not used, it’s relatively cheap but also ecologically sound. Construction regulations permit this type of application, but the effect fly ash has on the ground underneath it is unknown.

“Fly ash is a byproduct of burning coal, and as such, it contains some heavy metals and other chemicals,” says Benson. “The question is, how much of that will leach out of stabilized soil and potentially contaminate ground water?”

Benson and his team believe that the effect is, if any, very small, as their laboratory tests indicate, but the experiment at the development in Cross Plains will show the exact effect over a long period of time.

The project included installing a lysimeter, an instrument for measuring the water percolating through soils and determining the materials dissolved by water.

“An objective of this research is show that this method of construction is safe and effective,” says Benson. “If we can stabilize the soil in place with fly ash, it saves money and natural resources. Using fly ash also prevents it from being placed in a landfill.”

In a second field experiment on a 4,000-foot segment of Highway 60, the team is experimenting with nine new and inexpensive ways to stabilize the road’s soft, muddy clay subgrade. The project includes fly ash and bottom ash, a gravel-like byproduct of coal burning, and two foundry byproducts: foundry slag and foundry sand. Five remaining segments will test geosynthethic fabrics that reinforce soil by a factor of 12 to 15. Once these stabilization materials are in place, a layer of crushed rock and asphalt will be added.

These sections, which are placed between control sections, include various types of instrumentation like the lysimeters used in Cross Plains. Moisture and temperature probes will test conditions of the test sections, and other gauges measure the force of traffic on the geosynthethic materials. During the construction process, soil stiffness and dynamics are tested.

The results of the university’s research should offer state transportation officials and industry important knowledge that enable them to build safer, stronger roads while creating a beneficial use for waste.