STUDY ON CRUSHING PROCESS AND MICROSCOPIC MECHANISM OF CALCAREOUS SAND
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摘要: 为了掌握南海钙质砂压缩变形特征及其微观机制,对3种不同粒组(S1:1.43~2mm、S2:0.5~1mm、S3:0.5~2mm)的钙质砂进行100~3200kPa压力范围的压缩试验,利用自制的砂土微观结构提取装置和图像处理软件(PCAS)获得并分析了钙质砂压缩过程中微观结构。结果表明:(1)钙质砂的大小、形状和级配对颗粒的破碎具有显著影响,当压力较低时(<800kPa),粒径较大的S1组以砂颗粒棱角破碎为主;粒径较小的S2组没有明显破裂,相对规则的颗粒形态使S2粒组在该压力范围内主要因颗粒的滚动与重分布导致压缩;级配良好的S3组除部分低宽度断肢状颗粒外其余大小、形态颗粒无明显破裂。(2)当压力较大时(>800kPa),S1组钙质砂逐渐转向以颗粒的整体破坏为主的破碎形式;S2、S3两组试样随着密实度的提高,砂颗粒的破坏以整体破碎为主。基于对破碎过程中试样微观结构变化的提取与分析,总结并提出了控制钙质砂颗粒破碎的4种接触模式:点-线接触、线-面接触、面-面接触和复合接触,可用于判断不同条件下的颗粒破碎形式。最后,讨论了钙质砂在破碎过程中颗粒几何参数的变化。Abstract: In order to grasp the compression characteristics and microscopic mechanism of calcareous sand in the South China Sea, we did compression tests on three different groups of calcareous sand(S1:1.43~2mm, S2:0.5~1mm, S3:0.5~2mm). We used a self-made sand microstructure extraction device to obtain the microstructure of calcareous during compression. The results indicate that:(1)The size, shape and grade of the calcareous sands significantly affect the fracture of the particles. When the pressure is lower than 800kPa, the S1 group with large particle size is mainly broken by the angular break of the sand particle; but the S2 group with smaller particle size does not have obvious cracks. That's means relatively regular particle morphology leads S2 group to compress mainly by rolling and redistribution of the particles. For the well-graded S3 group, particles have no obvious cracks except for some low-width broken limb-shaped ones. (2)When the pressure is larger than 800kPa, S1 group of calcareous sand turns to the broken form dominated by the overall destruction of the particles; S2, S3 with the increase of the compactness, the damage of the two groups of calcareous sand sample is dominated by the overall fragmentation of the particles. Based on the microstructure changes of these different groups of calcareous sands during the compression, we summarized four contact modes which control the crushing of calcareous sands: point-line contact, line-surface contact, surface-surface contact and composite contact. These contact models can be used to determine the form of particle breakage under different conditions. Finally, we discussed the effect of crushing process on the geometry parameters of calcareous sands.
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Key words:
- Calcareous sand /
- Compression test /
- Particle breakage /
- Microstructure
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表 1 各粒径砂颗粒基本几何参数
Table 1. Basic geometric parameter of various particle size
粒径
范围
/mm平均
周长
/mm最大
长度
/mm平均
长度
/mm最大
宽度
/mm平均
宽度
/mm平均
长宽比平均
形状
系数0.5~1 2.57 1.68 0.91 0.94 0.61 1.49 0.73 1~2 5.31 3.59 1.89 1.65 1.2 1.58 0.70 表 2 各粒组颗粒统计参数
Table 2. Sand sample particle statistical
粒组 压力
/kPa最大长度
/mm平均长度
/mm最大宽度
/mm平均宽度
/mm形状
系数S1粒组 100 1.45 0.60 0.62 0.27 0.43 200 0.91 0.43 0.45 0.18 0.39 400 1.54 0.65 0.74 0.32 0.40 800 0.97 0.32 0.57 0.17 0.46 1600 1.92 0.85 0.79 0.36 0.44 3200 0.77 0.29 0.38 0.13 0.50 S2粒组 100 1.07 0.42 0.59 0.20 0.49 200 1.12 0.54 0.60 0.25 0.41 400 0.56 0.29 0.30 0.15 0.45 800 0.99 0.45 0.53 0.21 0.46 1600 0.57 0.24 0.29 0.12 0.46 S3粒组 100 1.40 0.65 0.56 0.28 0.48 200 1.34 0.72 0.62 0.32 0.50 400 0.77 0.29 0.36 0.13 0.40 800 0.82 0.31 0.45 0.14 0.43 1600 0.79 0.27 0.39 0.12 0.43 3200 0.77 0.26 0.40 0.12 0.46 -
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