Use of X-Bar and R Control Chart Methods on Long-Term Piezometer Data for Sinkhole Assessment

Extreme rainfall events, such as tropical storms and hurricanes, can produce large amounts of precipitation in a short period of time. In Central Florida where a relatively thick impermeable soil layer (i.e., Hawthorn Clay) is present, a differential water pressure head causes internal soil erosion that can become a catalyst in the creation of sinkholes. To better determine the likelihood of such formations, long-term piezometric data were analyzed to identify abnormal behavior of groundwater where the erosion process is significant. In this study, X-Bar and R control chart, commonly used for quality control in many industries, were employed. The X-Bar chart was used to determine the variation of distinct point averages when compare to an overall system average and R chart looks at the range of individual locations over a given time frame and compares that to the average range of a system. A significant variance in range of a specific point when compared to nearby sensors can help identify ground water flow and possible anomalies. This sensor instrumentation and analysis method was applied to the Wekiva Parkway SR46 connector project in Central Florida. Through analyzing a system of piezometers over a specific time frame in which one or more extreme weather events occur, these management tools could identify abnormal-behavior piezometer locations where the potential of future sinkholes could occur due to active internal soil erosion; thus, preventative monitoring and/or mitigation are necessary.