(a) Schematic diagram of the experimental setup for the seepage test under Darcy’s law. (b) Saturation process of group syringes in a vacuum desiccator. The purple arrow represents the direction of flow through porous media. (c) GSDs of glass beads (purple) and quartz sand (blue) measured by sieving analysis. (d) Glass beads (at a magnification of 50×) under scanning electron microscopy (SEM). The dark area represents the top of the SEM pin stub, whereas the particle surface is highlighted in greyish-white