Erosion Rate Prediction Model for Levee-Floodwall Overtopping Applications in Cohesive Soils

Abstract

Floodwall overtopping erodes the levee surface. Characterizing the erosion rate of levee-floodwall systems is crucial for designing such structures. Scouring as a result of overtopping during storm events, is one of the major reasons for the failure of these structures. In this study, the contributing factors such was floodwall height, soil characteristics, and hydraulic characteristics of overtopped flow are considered to develop an erosion rate prediction model for such structures built with fine-grained soils. Using over 60 simulated scaled levee-floodwall test results, the effect of the contributing parameters on soil erosion described and quantified. The tests cover relatively wide ranges of soil plasticity index (0% to 40%), degree of compaction (70% to 90%), saturation ratio (15% to 85%), scale of the floodwall (1:20 to 1:2), and overtopped flow velocity (0.2 m/sec to 0.6 m/sec). The scouring mechanism in the soil with low plasticity indices (0% to 9%) developed scouring hole, and by increasing the saturation ratio, erosion rate increased significantly. However, in the soil samples with high plasticity indices (i.e., 30% and 40%) a scour hole development is less pronounced and erosion rates decrease by increasing the saturation ratio. Utilizing the lab-scaled simulation results, a prediction method was developed to estimate erosion rates based on other soil and hydraulic properties. The developed model was validated using case history and compared to other prediction methods