Analysis of Transient Seepage Through Levees

Levees are a significant part of the United States flood protection infrastructure. It is estimated that over 100,000 miles of levees exist in the United States. Most of these levees were designed many years ago to protect farmland and rural areas. As growth continues in the United States, many of these levees are now protecting homes and other important structures. The American Society of Civil Engineers gave the levees in the United States a grade of Din 2009. To bring flood protection up to modern standards there requires adequate methods of evaluating levees with respect to seepage, erosion, piping and slope instability. Transient seepage analyses provide an effective method of evaluating seepage through levees and its potentially destabilizing effects. Floods against levees usually last for days or weeks. In response to a flood, pore pressures within the levee will change from negative (suction) to positive as the phreatic surface progresses through the levee. These changes can be calculated by finite element transient seepage analyses. In order for the transient seepage analysis to be valid, appropriate soil properties and initial conditions must be used. The research investigation described here provides simple and practical methods for estimating the initial conditions and soil properties required for transient seepage analyses, and illustrates their use through a number of examples.