Three-dimensional Wadell roundness for particle angularity characterization of granular soils
Three-dimensional Wadell roundness for particle angularity characterization of granular soils
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DOI：
10.1007/s11440-020-01004-9
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发表时间：
2020-06-23
期刊：
影响因子：
5.7
通讯作者：
Alimohammadi, Hossein
中科院分区：
文献类型：
--
作者：
Zheng, Junxing;He, Hantao;Alimohammadi, Hossein
地质学家哈肯·瓦德尔（Hakon Wadell）在20世纪30年代提出了圆度定义，用于量化颗粒状土壤的颗粒角度。由于在20世纪30年代难以获得三维（3D）粒子几何形状，Wadell使用粒子的二维（2D）投影来发展他的圆度定义，尽管它在分析三维粒子时受到限制。本研究表明Wadell的二维圆度可以扩展到三维定义。三维圆度定义为与三维粒子的角和脊相匹配的球体的平均半径与该三维粒子的最大内切球体的半径之比。提出了一种自动识别角脊的计算几何算法，将合适的球与角脊匹配，识别三维粒子的最大内切球，计算三维圆度。为控制球体拟合过程，定义了颗粒的最大内切球体NSD的每直径的切片数。建立最小要求nsd = 300，以确保所提出的三维计算几何算法的可靠使用。最后，利用x射线计算机断层扫描技术对5个不同角度的沙粒进行扫描。比较了这2万个粒子的二维和三维圆度。二维圆度捕获了相应三维圆度的总体趋势，但变化范围较大，导致使用二维图像推断三维粒子角度时存在较大的不确定性。
The geologist Hakon Wadell proposed the roundness definition in the 1930s for quantifying the particle angularity of granular soils. Due to the difficulty in obtaining three-dimensional (3D) particle geometries in the 1930s, Wadell used two-dimensional (2D) projections of particles to develop his roundness definition, although it is limited for analyzing 3D particles. This study shows that Wadell's 2D roundness could be extended to a 3D definition. The 3D roundness is defined as the ratio of the average radius of spheres fitting to corners and ridges of a 3D particle to the radius of the maximum inscribed sphere of the 3D particle. A computational geometry algorithm is proposed to automatically identify corners and ridges, fit appropriate spheres to corners and ridges, identify the maximum inscribed sphere of the 3D particle, and compute 3D roundness. The number of slices per diameter of the maximum inscribed sphere of the particle,NSD, is defined for controlling the sphere fitting process. The minimum requiredNSD = 300 is established to ensure the reliable use of the proposed 3D computational geometry algorithm. Finally, a total of 20,000 particles from five sand specimens with various angularities are scanned by X-ray computed tomography. The 2D and 3D roundnesses of these 20,000 particles are compared. The 2D roundnesses capture the general trend of the corresponding 3D roundnesses, but vary in a large range, resulting in significant uncertainties when using 2D images to infer 3D particle angularities.