Morphological characteristics of carbonate soil in South China Sea based on dynamic image technology
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摘要: 颗粒形态是一项重要的细观指标,影响着粒状土的物理力学性质。钙质土因为其特殊的生物成因,有着复杂的颗粒形态。为了研究其颗粒形态特征,采用PartAn 3D颗粒动态图像分析仪对粒径0.5~20 mm的南海钙质土颗粒开展形状测试,采用延伸率、扁平度、球形度、圆度、棱角度和凸度指标定量描述颗粒形态特征。结果显示:南海钙质土颗粒的延伸率、扁平度、球形度和圆度符合正态分布,而棱角度和凸度符合幂律分布;颗粒形状以块状居多,随着粒径的减小,钙质土颗粒变得更扁平,形状更规则;通过研究样本数量对颗粒形状量化结果的影响,建议采用形状指标的算术平均值量化单一粒组钙质土颗粒形状特征时,颗粒数目不少于600。最后,运用统计学中的主成分分析方法,得到一个综合考虑钙质土颗粒形状信息的新指标,建立了该指标与钙质土最大、最小孔隙比的关系。Abstract: The particle morphology is an important microscopic characteristic that affects the physical and mechanical properties of granular soils. Carbonate soil particles have complex morphology due to special biogenesis. In order to study the morphological characteristics of the soil particles, the PartAn 3D particle dynamic image analyzer was used to test the particle shape of the carbonate soil with grain sizes of 0.5 ~ 20 mm from the South China Sea. The elongation, flatness, sphericity, roundness, angularity and convexity were used to quantitatively describe the morphological characteristics of the particles. The results show that the frequency distribution of the elongation, flatness, sphericity and roundness of carbonate soil particles in the South China Sea complies with the normal one, while the frequency distribution of the angularity and convexity complies with that of the power law. The particle shape of the carbonate soil is mostly blocky, and with the decrease of grain size, the soil particles become flatter and more regular in shape. Through investigating the effects of sample size on the results of particle shape quantification, it is suggested that the number of particles should be not less than 600 when using the arithmetic mean of shape descriptors to quantify the morphological characteristics of the uniformly graded carbonate soil. Finally, a comprehensive shape index which can fully describe the morphological characteristics of the carbonate soil particles is obtained with the aid of the principal component analysis method in statistics, and the relationship between this shape index and the maximum to minimum void ratio of the carbonate soil is established.
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Keywords:
- carbonate soil /
- dynamic image technology /
- particle shape /
- maximum void ratio /
- minimum void ratio
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表 1 本文选用的表征颗粒形状特征的指标
Table 1 Indices chosen to characterize particle shape in this paper
指标 定义 取值范围 描述特征 延伸率 FW/FWFLFL 0~1 宏观形状。颗粒越狭长,其值越小 扁平度 FT/FTFWFW 0~1 宏观形状。颗粒越扁平,其值越小 球形度 (Da/Dp)2 0~1 宏观形状、中观棱角。颗粒越接近球形,其值越大 圆度 4A/(π F2L) 0~1 宏观形状、中观棱角。颗粒越接近圆形,其值越大 棱角度 A/AC 0~1 中观棱角。颗粒棱角越多,越突出,其值越小 凸度 PC/P 0~1 细观纹理。颗粒表面越光滑,其值越大 注:Da为与颗粒投影图像等面积圆的直径;Dp为与颗粒投影图像等周长圆的直径;FL,FW和FT分别为Feret长度、宽度和厚度;A为颗粒投影图像面积;P为颗粒投影图像周长;AC为颗粒投影图像外接最小凸边形面积;PC为颗粒投影图像外接最小凸边形周长。在本次试验中,Da,Dp,A,P,AC和PC取一系列图像的平均值;FL取一系列图像中的最大长度,FW取一系列图像中的最大宽度,FT取一系列图像中的最小宽度。 表 2 不同粒组钙质土颗粒形状指标统计表
Table 2 Statistical list of particle shape indices of carbonate soil with different grain fractions
粒组 统计量 延伸率 扁平度 球形度 圆度 棱角度 凸度 10~20 mm 平均值 0.667 0.689 0.794 0.471 0.954 0.979 中位数 0.681 0.703 0.806 0.475 0.961 0.984 最小值 0.219 0.162 0.389 0.144 0.730 0.814 最大值 0.947 0.990 0.961 0.854 0.998 0.998 标准差 0.125 0.159 0.081 0.112 0.031 0.017 5~10 mm 平均值 0.670 0.668 0.808 0.471 0.961 0.985 中位数 0.683 0.673 0.818 0.473 0.966 0.988 最小值 0.233 0.162 0.254 0.070 0.543 0.802 最大值 0.945 0.988 0.978 0.857 0.997 0.999 标准差 0.123 0.149 0.071 0.104 0.026 0.012 2~5 mm 平均值 0.685 0.629 0.806 0.460 0.960 0.990 中位数 0.699 0.649 0.818 0.461 0.967 0.993 最小值 0.096 0.105 0.153 0.047 0.599 0.874 最大值 0.963 0.967 0.979 0.826 0.999 1.000 标准差 0.120 0.175 0.081 0.111 0.030 0.009 1~2 mm 平均值 0.686 0.635 0.834 0.461 0.972 0.995 中位数 0.698 0.649 0.848 0.465 0.980 0.997 最小值 0.109 0.235 0.300 0.051 0.667 0.893 最大值 0.963 0.956 0.980 0.827 1.000 1.000 标准差 0.114 0.147 0.075 0.113 0.026 0.006 0.5~1 mm 平均值 0.684 0.605 0.850 0.424 0.987 0.998 中位数 0.692 0.607 0.859 0.432 0.992 0.999 最小值 0.153 0.202 0.283 0.055 0.693 0.945 最大值 0.934 1.000 1.000 0.744 1.000 1.000 标准差 0.115 0.118 0.059 0.098 0.018 0.003 表 3 量化钙质土颗粒形状特征所需的最小样本数量
Table 3 Minimum number of samples required to quantify shape characteristics of carbonate soil particles
粒组 延伸率 扁平度 球形度 圆度 棱角度 凸度 10~20 mm 345 446 238 344 14 10 5~10 mm 326 583 135 292 12 10 2~5 mm 270 439 121 224 32 10 1~2 mm 111 473 68 136 17 10 0.5~1 mm 318 241 77 242 10 10 表 4 不同粒组钙质土的极限孔隙比
Table 4 Limit void ratios of carbonate soil with different fractions
孔隙比 10~20
mm5~10
mm2~5
mm1~2
mm0.5~1
mmemax 2.225 1.821 1.703 1.576 1.456 emin 1.586 1.241 1.143 1.138 1.112 注:emax为最大孔隙比;emin为最小孔隙比。 表 5 现有预测极限孔隙比的经验公式
Table 5 Existing empirical equations for predicting limit void ratio
文献 经验公式 Santamarina等[3] emax=0.554+0.154R−1,emin=0.359+0.082R−1 Cho等[5] emax=1.5−0.41(R+S),emin=0.9−0.22(R+S) Patra等[22] emax=0.6042D50−0.304,emin=0.3346D50−0.491 Zheng等[23] emax=R−0.20S−0.25Cu−0.10e∘max,emin=R−0.15S−0.25Cu−0.50e∘min Hryciw等[24] emax=0.50R−0.2+0.41S−0.6+0.34Cu−0.2−0.51,emin=0.37R−0.2+0.28S−0.6+0.31Cu−0.3−0.48 Chang等[25] emax=0.619R−0.372(D50/Dref)−0.048,emin=0.413R−0.291(D50/Dref)−0.043 注:e∘max为参考最大孔隙比,等于0.75;e∘max为参考最小孔隙比,等于0.50;Dref为参考粒径,等于1 mm。 表 6 方差贡献率表
Table 6 Variance contribution rates
成分 特征值 方差贡献率/% 累积方差贡献率/% 1 3.698 92.455 92.455 2 0.238 5.942 98.397 3 0.060 1.488 99.886 4 0.005 0.114 100.000 -
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