CEE professors engage in groundbreaking soil stabilization research
It's hard to find Civil and Environmental Engineering Professors Craig Benson and Tuncer Edil behind their desks. You have a better chance of locating them on a construction site, actively participating in the task at hand. They prefer to teach through hands-on lessons, likes those found in their groundbreaking soil stabilization research efforts.
Benson and Edil are currently involved in two major projects that are resulting in environmentally safe and cost-effective roadbed construction. They are testing the effect of fly ash on ground water at a road construction site in Cross Plains and helping Wisconsin's Department of Transportation create a more durable surface on Highway 60 near Lodi. This summer, they shared the progress and plans for their research.
The newly paved roads in the Scenic Edge development in Cross Plains were once muddy pathways that made it difficult to move heavy construction machinery. Because the soil was very moist, contractors needed to take extra measures to stabilize the soil under the new streets. Typically, this would call for the wet soil to be removed and replaced with crushed rock-a time consuming and very 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 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," said 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. The lysimeter was equipped with a tank from which samples will be collected for chemical analysis. Water runs into the tank via a pipe that's attached to a 15-inch deep, 200 square foot basin. The basin, which lies under the surface of the development's main thoroughfare, was lined with a polyethylene geomembrane, a heavy duty, flexible plastic. On top of that, they placed a geocomposite drainage mat that allows fluid to flow through the basin's drain, down the pipe and into the tank. The entire system was covered with dirt and the fly ash-fortified roadbed was built over it.
"An objective of this research is show that this method of construction is safe and effective," said Benson. "We hope that fly ash will be used more frequently because of its advantages. In a situation like this, at least one meter of soil would need to be quarried out and moved to a different location and replaced with expensive crushed rock. 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."
About 20 miles north of Cross Plains, Benson and Edil are working on 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. The five remaining segments will test different 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.
One of the geosynthethics being tested is Geoweb(r), a material manufactured in Appleton, Wisconsin by Presto Products Company that confines soil in its honeycomb-like structure. "The Geoweb(r) cellular confinement system was developed by Presto about 20 years ago with the Army Corps of Engineers and brought into public sector in the mid 80s," said Daniel Senf, Presto's global sales and marketing manager and a Michigan Tech graduate. "Now, it's used all over the world-even during Desert Storm-to build roads more cost effectively when soils can't support the anticipated loads. The University of Wisconsin-Madison's research will prove to the State of Wisconsin that this is a viable solution to base stabilization and load support problems."
These sections, which are placed between control sections, are filled with 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, various tests are completed to test soil stiffness and dynamics. These measurements, combined with visual examination of distress over the years, will determine if these materials perform as expected by providing a stable base for construction.
"This experiment will help us develop construction guidelines and specifications so highway engineers know what technical performance to expect from these products," said Edil. "They can use this information along with an economic analysis and can decide which of these materials can best aid them in construction of new highways. We will determine the equivalency of a smorgasbord of soft subgrade stabilization options."
The soil stabilization research projects in Cross Plains and on Highway 60, which are sponsored in part by the State of Wisconsin Department of Transportation, Alliant Energy, Northern States Power, Mineral Solutions, Inc., Grede Foundries, Presto, Tenax and Amoco, benefit all parties involved. For companies like Presto, the university offers an unbiased testing and evaluation center that will offer credible evidence in support of their product. The university, in turn, has the opportunity to conduct research on state-of-the-art materials and practices that allow it to better educate its students. The results of the university's research offer the State of Wisconsin DOT important knowledge that enables it to build safer, stronger roads for Wisconsin travelers and offer state foundry and power industries a beneficial use for their byproducts.