An out-of-the-box approach to a competition held entirely within a sand-filled container earned a group of University of Kansas School of Engineering students high honors at a national geotechnical conference.
Graduate students Jun Guo, Shenzhen, China, and Xiaohui Sun, Nanjing, China, and civil engineering undergraduate students Jennifer Penfield, Shawnee, and Lee Crippen, Olathe, won second place in the American Society of Civil Engineers National GeoWall competition, which was March 3-6 in San Diego. The team traveled to San Diego with a group of other students and professors from the KU Geotechnical Society.
Here’s how the challenge works: Each team has a 26-inch-by-18-inch-by-18-inch wooden box with one removable side. Teams are timed while they cut Kraft paper strips, construct a poster board wall, insert the reinforcing paper strips and place the wall inside the wooden box. As sand is poured into the box, teams compact it and arrange the paper strips in layers. Once the box is full, the removable side is taken away, leaving the poster board to serve as one wall of the box.
The paper strips hold the key to the stability of the poster board. Each team prepares an original design of how to cut the Kraft paper strips and weave them through the poster board.
“The common design uses the friction between paper strips and sand to keep the wall in place. When the weight of the sand presses into the wall, the friction holds the wall in place,” said Guo, a first-year master’s student in civil engineering with a geotechnical emphasis. “Instead of laying our paper flat, we decided to lay the strips out in loops, so the sand trapped within each loop is almost like a solid object and is held firmly in place. The friction between sand particles is much higher than that between sand and paper.”
Once the box is full, a series of tests are run to gauge strength and stability of each team’s GeoWall. The first test is to remove one side of the box and test the poster board wall’s ability to hold the sand for one minute without excessive deflection or failure. For the second test, a 50-pound bucket of sand is placed on top of the box to test the wall’s stability against vertical loading. The wall must hold for one minute with minimal deflection. Stability against a horizontal load is tested by hanging a bucket from a support arm grounded in the sand, adding 20 pounds of sand, and timing the wall to stand on its own for one minute with minimal deflection. The wall then undergoes a dynamic-loading test, which consists of dropping a 5-pound weight onto the support arm holding the 20-pound bucket.
“We were really happy with our wall. The weight was dropped six times before our wall finally failed,” said Penfield, a senior.
The KU GeoWall team had to submit a preliminary report on its design – and scored high enough to be among 16 teams selected to participate in the national competition. The Jayhawk team, led by faculty adviser Professor Jie Han, spent more than three months preparing, practicing hours each week, but one critical change in components made the competition a little trickier.
“There was a big difference in the sand we used for practice and the sand they had at the competition,” Guo said. “Theirs had big particles. At KU, we use Kansas River sand, which is finer. It actually worked to our benefit because it’s more challenging for the paper strips to hold the wall with the finer particles.”
The GeoWall competition provides valuable experience for situations engineers may encounter in the field.
“This is real-world stuff. This is how you’d actually stabilize a slope,” Penfield said. “It’s great to apply what we’ve learned into something we can build."