QUANTITATIVE EVALUATION OF SAND SHAPE AND ROUNDNESS AND THEIR POTENTIAL EFFECT ON STABILITY OF SAND-BASED ATHLETIC FIELDS

Playing surface stability can be a problem when sand-based media are used in sports fields. Many factors, such as particle size, particle size gradation, shape, roundness, water content, and plant materials may affect surface stability. The relative importance of these factors in surface stability is not clearly understood. The primary objective of this study was to evaluate shape and roundness of sand particles quantitatively so they can be compared with other factors in terms of their contributions to surface stability. 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 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 of 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 of 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 determining the differences among materials. Two-dimensional image analysis, which returns form factor, roundness, and aspect ratio, provided insufficient separation of the diverse sands evaluated in this study.