Field investigation of a sand boil developed during the Mississippi River flood of 2011

In the spring of 2011, the Mississippi River experienced historic flooding on a scale not experienced since the floods of 1927 and 1937. After the flood waters receded, researchers from the U.S. Army Engineer Research and Development Center (ERDC) and the U.S. Army Corps of Engineers, Vicksburg District (CE-MVK) investigated a site in Winterville, Mississippi, where a high-energy sand boil had developed during the flood. The purpose of the investigation was to gather field data and use these data to identify conditions produced from the formation of the sand boil. The ERDC/MVK team collected data using two methods: Cone Penetration Tests (CPT) and excavation of a trench. The trench was used to examine a low density area identified from CPT soundings and to visually describe the soil conditions below the surface. Field data collected at the Winterville site revealed that blanket thickness anomalies can be localized. The data also showed that minor geologic discontinuities were exploited by underseepage forces. Clay spherules mixed with sand were found below the area of low density as well as in the sand boil ejecta. Based on the disturbed soil profile and the clay spherules, seepage associated with sand boils can be turbulent in nature.