Experimental study on the 3D geometric characteristics of backward erosion pipes

Understanding the geometric dimensions of pipes formed during backward erosion piping (BEP) is crucial for comprehending the BEP mechanism and conducting numerical simulations. However, current research primarily focuses on the two-dimensional morphology of pipes, with a lack of sufficient understanding regarding their three-dimensional (3D) characteristics. To study the 3D geometric characteristics of the pipe, the 3D size of the pipe was measured and analyzed using the gypsum injection method and 3D laser scanning method in this study. The variations in pipe depth, width, and the ratio of width to depth were investigated in detail. And the influence of cover plate roughness and sand compactness on the 3D geometry of the pipe was clarified. It is found that the cross-section shape of the pipe is approximately rectangular, with the horizontal scale being significantly larger than the vertical scale. With increasing distance from the outlet hole, there is a gradual decrease in both the depth and width of the pipe. The relationship between the pipe's depth and width with respect to its length can be described using linear functions. As the compactness of sand layer increased, the depth and width of the pipe decreased to a certain extent.