Dam-break dynamics of transparent granular media in water using multi-sectional visualization

Many geotechnical hazards involve complex interactions between soil and water, such as those seen in levee failures, scour, and underwater landslides. Predicting these phenomena accurately requires validation through physical experiments. In this study, a two-dimensional dam break experiment was performed using transparent ellipsoidal particles with a refractive index close to that of water. This setup enabled the clear visualization of the particle behavior in the near-wall and interior regions without the use of viscous fluids. Laser sheet illumination was applied to multiple cross sections, and high-speed imaging with particle image velocimetry (PIV) was employed to quantify the three-dimensional flow behavior. The velocity and flow thickness varied between the wall and the channel center, indicating depth-wise differences in the collapse mechanism of the granular material. These results demonstrate the effectiveness of using transparent particles and water for visualizing internal flow. They also provide valuable benchmark data for validating high-resolution numerical models, such as the discrete element method and smoothed particle hydrodynamics. Although the particle density differed slightly from that of natural soil, the experimental setup captured coupled flow phenomena, including the Darcy flow and Navier-Stokes flow. Thus, this study lays the foundation for future work using particles that are smaller in size and have natural soil density, leading to an improvement of our understanding of submerged granular flows.