Mason sand, concrete sand, silica sand, crushed brick, and crushed stone were used in this study to cover a wide range of shapes and roundness based on visual observation. In order to test the methodology, we used glass beads as the base line. We also crushed glass to make a very angular sample. All materials were washed free of silt- and clay-sized particles and oven dried before use in evaluation. A roughness index (I_r) was proposed as the ratio of the particle surface area to the area of a sphere of the same volume. Surface areas were determined by coating the materials with aniline blue dye and measuring the light absorption of the dye washed off the particle surface. Angle at repose, coefficient of uniformity (CU), coefficient of friction (CF), and two-dimensional image analysis were also included in the evaluation of the materials.

Principle component analysis indicated that only three factors – angle at repose, CU, and I_r,– are necessary to explain 98.5% of the variance contributing to surface stability of sand-based media. The results of this study showed that shape and roundness of sand grains could be expressed by I_r, which is sensitive and convenient for picking out the differences between materials. Two-dimensional image analysis, which returns form factor, roundness, and aspect ratio, provided insufficient separation of the diverse sands evaluated in this study.

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Table 1. A comparison of the effectiveness of different factors for bulk samples in predicting sand stability.