Geometric Characteristics of Shrinkage Crack Network in Soil
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摘要: 通过室内试验研究了土壤干缩裂缝发育规律，采用数字图像处理技术与AutoCAD测量功能，分析了不同含水率下土壤裂缝网络几何形态特征.结果表明：土壤含水率达到43%时出现裂缝，裂缝骨架长度、周长和面积分别在含水率达到23%、23%、7%时趋于稳定，裂缝平均宽度的发育经历了波动增长、线性增长和稳定3个阶段，并在含水率达到7%时保持不变；裂缝条数与节点数之比随含水率降低而减小，并最终保持在1.67，此结果与收缩块区分散度和裂缝交叉角度分布规律共同表明，裂缝网络形态呈方形正交网络分布趋势，且处于方型网络与“T”型正交网络之间；裂缝平均弯曲度随含水率减小，由1.06减小至1.02并保持恒定，揭示了裂缝整体弯曲程度与不同时期裂缝弯曲的变化规律.Abstract: An indoor experiment was conducted to investigate the development law of the shrinkage crack network in soil in this study. By application of digital image processing technology and the measurement functions of AutoCAD, geometric characteristics of shrinkage crack network were quantitatively analyzed under different moisture contents. The results show that the crack first was initiated when the moisture content was 43%. The length of crack skeleton and crack perimeter began to stabilize once the moisture content was close to 23%, and so did the crack ratio at the moisture content of 7%. The average width of the crack developed in three stages, namely, fluctuation growth, linear growth and stabilization, which reached a stable value as the moisture content came to 7%. The ratio of the crack fragments and intersections decreased as the moisture contents became lower and remained stable at 1.67 ultimately, which, together with dispersity of the aggregate and frequency distribution of intersection angles, revealed the square network distribution trend of the crack network. The mean tortuosity of the crack was reduced from 1.06 to 1.02 with the moisture content dropped and stabilized at 1.02, which indicates the whole tortuosity of the cracks and the variation law of the crack tortuosity during different periods.
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Key words:
- soil /
- crack /
- network /
- geometric characterization /
- soil testing
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图 3 土壤含水率、蒸发强度随累积时间变化规律
Fig. 3. Changes in water content and evaporation rate of soil in relation to the accumulated drying time
图 5 裂缝骨架总长度、裂缝总周长、裂缝平均宽度与含水率关系曲线
Fig. 5. Changes in the total length of the crack skeleton, crack perimeter and average width of the crack in relation to the water content upon drying
图 6 4个典型阶段裂缝交叉角度频次分布
Fig. 6. Frequency distribution of intersection angles in four typical stages
图 9 不同含水率下裂缝条数与网络节点数比值
Fig. 9. Relations between the numbers of segments and intersections in the crack networks under different water content
表 1 土壤试样物理性质
Table 1. Physical properties of tested soil
试样土壤种类 颗粒粒径分布(%) 容重(g·cm-3) 土壤质地 > 0.02 mm 0.02~0.002 mm < 0.000 2 mm 水稻土 31.29 23.49 45.23 1.56 粘土 
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表 2 规则图形分散度
Table 2. Dispersity of the regular geometrical patterns
形状 正三角 矩形 黄金矩形 正方形 分散度 20.78 18.00 16.94 16.00 形状 正五边形 正六边形 正八边形 圆形 分散度 14.52 13.86 13.32 12.57 注：矩形长宽比为2∶1，黄金矩形长宽比约为1.618.
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表 3 裂缝条数与节点数统计以及二者的比值
Table 3. Numbers of the crack fragments and intersections and their ratio
含水率(θ) 裂缝条数(S) 节点数(I) 比值(S/I) 31.62 13 4 3.250 29.32 38 17 2.235 27.70 62 33 1.879 25.28 99 57 1.737 22.58 111 67 1.657 21.36 114 69 1.652 18.85 118 70 1.686 16.22 114 69 1.652 15.09 115 69 1.667 12.89 117 70 1.671 9.86 116 69 1.681 7.23 116 69 1.681 6.05 115 70 1.643 4.48 115 69 1.667 3.80 116 7 1.657
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