Microscopic investigation of the occurring process of contact erosion

Sand particles subjected to seepage can cause contact erosion because of particle migration. A visible seepage system packed with transparent sand optically matched oil, and a planar laser-induced fluorescence technique was used to visually study mechanisms during seepage-induced contact erosion. During the visualization experiments, two distinct contact erosion phenomena were observed. The first phenomenon is the common erosion phenomenon, which occurs in the entire sample range; it primarily manifests as the movement and migration of particles under the influence of the fluid, resulting in the loss of fine particles. The second phenomenon occurs in local areas of the sample and is characterized by particles being too large to pass through the pores; this leads to pore clogging, subsequently altering the seepage path and reducing the flow velocity. In addition, the effects of the hydraulic gradient and particle size on flow velocity and particle migration are analyzed. Preferential seepage paths are critical paths in the development of contact erosion. The force characteristics of the particles were investigated based on three types of instability modes and fitting curves to determine the stability of the soil structure considering the flow velocity and particle size. The findings in this study are through a visual experiment method to explain the instability modes and mechanism of particles in contact erosion and understand the relationship between particle migration and flow velocity.