Researchers from North Carolina State University have developed a sensor that allows engineers to assess the scour potential of soils at various depths and on-site for the first time – a technology that will help evaluate the safety of civil infrastructure before and after storm events. Scour, or erosion of soil around structures due to water flow, is responsible for a wide range of critical infrastructure failures – from unstable bridges to the levees that gave way in the wake of Hurricane Katrina.
“The ‘in situ scour evaluation probe’ (ISEP) is the first technology that allows technicians in the field to measure the scour potential of soils without the need for excavation,” says Dr. Mo Gabr, a professor of civil, construction and environmental engineering at NC State and co-author of a paper describing the new device. “Previous technologies required engineers to take samples and process them in a lab.”
Understanding scour potential is important because it can help authorities prepare for, or minimize the impact of, events such as the failure of the levees in the wake of Katrina. Scour has also been linked to approximately 60 percent of the bridge failures in the United States, as documented by the Federal Highway Administration.
“The ISEP’s ability to measure scour potential at different depths helps us predict how the soil will behave in the future as a support media, as various layers of soil are eroded or scoured,” Gabr says.
The ISEP will also allow end-users such as federal and state agencies and private consultants to perform scour assessment more frequently, since they will not have to take physical samples back to a lab for analysis. More testing data means researchers will have a larger data set to work with, which should help them to more accurately predict scouring rates and behavior.
The new probe uses a water jet to burrow a hole into the soil. Researchers can track the rate at which the water displaces the soil to determine the scour rate. Researchers can also manipulate the velocity and flow rate of the water to simulate various natural events – from normal stream flow to hurricane-induced surges.
The researchers plan to take the ISEP to North Carolina’s Outer Banks later this month to help with research efforts related to dune erosion.
The paper, “In Situ measurement of the scour potential of non-cohesive sediments (ISEP),” was presented Nov. 8 at the 5th International Conference on Scour and Erosion in San Francisco, Calif. The lead author is NC State graduate student Cary Caruso. The ISEP was developed under a grant from the U.S. Department of Homeland Security (DHS), as part of the work being done by the DHS Center of Excellence on Natural Disasters, Coastal Infrastructure and Emergency Management.
Note to Editors: The study abstract follows.
“In Situ measurement of the scour potential of non-cohesive sediments (ISEP)”
Authors: Cary Caruso, Mohammed Gabr, North Carolina State University
Presented: Nov. 8, 5th International Conference on Scour and Erosion in San Francisco, Calif.
Abstract: A vertical probe (VP) employing a water jet has been developed for assessing scour potential and erosion rates of sediments typically found at the bottom of rivers or streams. The probe for “In Situ measurement of the scour potential of non-cohesive sediments (ISEP)” is based on the idea that analysis of the probe penetration rate into the soil correlates with scour rate and erosion potential. The method proposed herein aims at measuring the potential scour rate in situ and as a function of depth. Results on test sands (mean particle diameter (D50 ~0.3mm) suggest that the rate of advancement of the probe is proportional to the vertical velocity of the water at the tip of the probe raised to a positive exponent. For the saturated sand used in testing, the exponent appears to be 1.4. The rate of embedment varies with moisture content. Thus far, scour rates determined with this proposed method are found to be in reasonable agreement with scour rates published for similar sands.