An Experimental Investigation on the Mechanism of Contact Erosion in Levee Foundations Considering the Characteristics of Particle Shape and Flow Field

Internal erosion is one of the most critical contributing factors for levee failures. Contact erosion, as a type of internal erosion, dominants when the seepage flow direction is parallel with the interface between coarse and fine soil layers. As is often the case beneath the foundation of a levee or at the top of clay core in an embankment dam, contact erosion can induce continuous transport of fine particles. Consequently, these water-retaining structures may collapse. To mitigate such potential hazards, the condition for initiation and progression of contact erosion should be investigated. In this research, the characteristics of contact erosion within cohesionless soils are presented visually by means of a newly devised apparatus. Two types of transparent coarse particles, namely quartz rubble and glass bead, are incorporated in two tests to study the effect of hydraulic conditions and particle shape on the initiation of contact erosion. The occurrence of contact erosion is captured qualitatively by snapshots, and the variation of soil sample configuration and flow lines are monitored by a stationary camera. Quantitative measurements are also conducted. Hydraulic gradients, turbidity, eroded mass, and inlet water pressure are recorded. The results provide insight into the influence of flow condition and particle shape on the occurence of contact erosion. The initiation and progression of contact erosion are governed by both hydraulic conditions and pore morphology. The latter is more crucial.