WASHINGTON - After years of development and laboratory testing, engineers are at the precipice of giving USACE Divisions and Districts a vital tool in protecting our nation’s critical levee systems and the lives and livelihoods those levees defend.
Developed and patented by researchers at the U.S. Army Engineer Research and Development Center (ERDC), the sand boil filter kit provides a quick, inexpensive and effective device to address small to medium sand boils that literally pop up, threatening the integrity of a levee.
Sand boils are caused when rising water levels on one side of the levee create erosion inside, forcing sand within the levee outward.
“A sand boil looks like a sand version of a volcano,” said Samantha Lucker, a research geologist with ERDC’s Geotechnical and Structures Laboratory (GSL). “A sand boil forms as sand is eroded from the foundation layer of the levee due to the change in water elevation on the upstream side. As the sand is carried up by water through the cohesive cover layer, it deposits on the side and that is what forms the boil.”
Lucker leads a team of GSL researchers that continues to develop and test the sand boil filter kit technology and create techniques for its use.
If unchecked, sand boils could grow, displacing more sediment and increasing the risk of a catastrophic levee breach. Internal erosion causes 46 percent of incidents and levee failures, Lucker said.
But why not just “plug” the sand boil?
“It doesn’t stop the pressure,” Lucker said. “If you plug the boil, another one will appear in another location.”
When detected, sand boils are often ringed with sandbags to raise the water level in the boil. By raising the hydraulic head, the horizontal hydraulic gradient is reduced, slowing and potentially stopping the erosion process altogether.
The downside to that traditional method is that it is slow, labor-intensive and requires a lot of transported material.
“We can do the same thing where a single person can go out with a lightweight filter, and it takes less than 15 minutes to get a good seal, check everything, make sure it is functioning correctly, and to make sure you have reduced the pressure across the system enough to reduce the erosion,” Lucker said. “And it’s something that can be reused again and again.”
According to estimates, deploying a reusable sand boil filter kit, is an estimated 114 times cheaper than sandbagging after the first use. A kit, complete with tools to install and replacement parts, is costs approximately $200, while the cost of sandbagging a small to medium-sized sand boil, six inches or less, costs thousands of dollars.
The filter kit can be installed by one person in 15 minutes, while ringing a sand boil takes a team of people and hundreds of sandbags.
Right now, five districts within the Mississippi Valley Division – Vicksburg, Little Rock, Memphis, St. Louis and Rock Island – are collaborating with the GSL team to test the kit’s existing design. The kit’s performance will be further tested in future flood events that cause sand boils, providing valuable data that will be used to further enhance its design.
With the support of ERDC’s Department of Public Works and research technicians, Lucker’s team has built the kits that have been deployed for testing, as well as additional kits staged at ERDC for use. If the field-testing results align with those recorded during extensive laboratory testing, the kits could be licensed for increased manufacturing as early as 2024.
“Any modifications are going to come from the districts and their valuable feedback,” Lucker said.
Lucker said the next step is to just wait for the next flood event and review the data.
“We want to get people excited about this technology, getting it out in the field, testing it and proving that it’s a concept that is functional,” she said. “If the field results support the laboratory data already collected, these kits will save time, will save money and will reduce the load on our districts.”