The particle shape of coral sand is a crucial factor that affects its accumulation characteristics. Two-dimensional particle images of coral sand with different particle sizes were obtained through optical imaging, and the basic size parameters of particles were measured by digital image processing. The particle shape parameters were created, and on this basis, the variation of shape parameters with size, the distribution characteristics, and the sensitivity of shape parameters were analyzed by mathematical statistics and the fractal theory. In addition, a comparative analysis was conducted for the particle shape and bulk density of coral sand and quartz sand with the same particle size. The results show that (1) for coral sand with particle size ranging from 0.5 to 5.0 mm, as the particle size augments, its overall profile coefficient grows, while the flatness, angularity, and roughness diminish and the particle shape deviates more from the regular circle. (2) The shape of coral sand particles exhibits good fractal characteristics, and the particle shape gets more complex as the particle size grows as evidenced by the fact that the fractal dimension enlarges. (3) All the shape parameters obey a skewed distribution. Concerning the sensitivity to the change in particle shape, the flatness occupies the first place, the overall profile coefficient and angularity come second, and the roughness ranks third, accordingly. It is suggested that flatness should be preferred as the evaluation parameter of the particle shape. (4) Compared with that of quartz sand, the particle shape of coral sand is more irregular, and the intergranular pores are larger under the same accumulation conditions, which is the primary reason why the specific gravity of coral sand is greater than that of quartz sand while the bulk density is smaller than that of quartz sand.

中文翻译：

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南海珊瑚砂的形状特征

珊瑚砂的颗粒形状是影响其堆积特性的关键因素。通过光学成像获得了不同粒径的珊瑚砂的二维颗粒图像，并通过数字图像处理测量了颗粒的基本尺寸参数。创建了颗粒形状参数，并在此基础上通过数学统计和分形理论分析了形状参数随尺寸的变化，分布特征和形状参数的敏感性。另外，对相同粒径的珊瑚砂和石英砂的颗粒形状和堆积密度进行了比较分析。结果表明：（1）粒径在0.5到5.0毫米之间的珊瑚砂，随着粒径的增加，其总体轮廓系数会增大，而平整度，棱角度和粗糙度减小，并且颗粒形状与规则圆的偏差更大。（2）珊瑚砂颗粒的形状表现出良好的分形特征，并且随着颗粒尺寸的增加，颗粒形状变得更复杂，这由分形维数增大这一事实证明。（3）所有形状参数均服从歪斜分布。关于对颗粒形状的变化的敏感性，平坦度居第一位，总轮廓系数和角度度居第二，粗糙度因此居第三位。建议将平整度作为颗粒形状的评价参数应优先考虑。（4）与石英砂相比，在相同的堆积条件下，珊瑚砂的颗粒形状更为不规则，且晶界孔较大；