The Development of Soil Cracks on Bunds in Purple Soil Sloping Farmlands and Its Influence on the Soil Shearing Strength
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摘要:目的 探究失水过程中埂坎的裂隙发育规律及其对抗剪强度的影响，为揭示埂坎失稳机制提供科学依据。方法 以典型紫色土坡耕地埂坎为研究对象，模拟试验埂坎土壤水分耗散和裂隙发育过程，测试土壤抗剪强度，分析土壤抗剪强度与裂隙发育的关系。结果 埂坎裂隙发育具有明显的阶段性特征，裂隙面积率、面积－周长比、形状指数和分形维数总体表现为先快后慢再趋于稳定。裂隙发育的阶段性对土壤抗剪强度及其参数的影响存在差异，快速发育阶段（31% ≥ w > 22%），裂隙发育和无裂隙发育试样的土壤抗剪强度、黏聚力和内摩擦角无明显差异；缓慢扩展和基本稳定阶段（22% ≥ w > 10%），裂隙发育通过影响土壤黏聚力对抗剪强度影响较大。试验条件下，裂隙发育试样的土壤抗剪强度总体小于无裂隙发育试样，土壤抗剪强度随含水率衰减而逐渐增大。裂隙发育和无裂隙发育试样抗剪强度的差异主要取决于土壤黏聚力，试验范围内的最小黏聚力（10.97 kPa）出现在质量含水率20%左右。裂隙发育试样的黏聚力随水分耗散的变化幅度不大，而内摩擦角则随水分耗散呈近似线性增大，裂隙发育试样的土壤抗剪强度主要受内摩擦角影响。结论 紫色土坡耕地埂坎土壤裂隙发育具有明显的阶段性特征，裂隙发育对埂坎土壤抗剪强度影响显著，且在低含水率时的影响更明显，埂坎土壤黏聚力受裂隙发育的影响较内摩擦角大。Abstract:Objective The aim was to explore the crack development law of the bund and its effect on the soil shearing strength in the process of moisture dissipating, and in order to provide a scientific basis for revealing the instability mechanism of the bund.Method A typical bund in purple soil sloping farmland was chosen as a case to explore the relationship between crack development and soil shearing strength through simulation experiments to observe the moisture dissipating and crack development process of the bund soil and test the soil’s shearing strength.Result The development of cracks on the bund had obvious stage characteristics, and the area ratio, area perimeter ratio, shape index and fractal dimension of cracks generally showed that they increased rapidly at first, then expanded slowly and tended to be stable. The stages of crack development had different effects on the soil shearing strength and its parameters. The shearing strength, cohesion and internal friction angle of the samples with crack development and no crack development had no significant changes in rapid development phase (31% ≥ w> 22%), while the crack development had a greater impact on the soil shearing strength and cohesion in the slow expansion and basically stable phase (22% ≥ w> 10%). Under the experimental conditions, the soil shearing strength of the samples with crack development was smaller than that of the samples without crack development as a whole, and the soil shearing strength gradually increased with the moisture dissipating. The difference between the shearing strength of the samples with cracks and no crack depended mainly on the soil cohesion. The soil cohesion tended to be a minimum (10.97 kPa) when the mass fraction of moisture content was at about 20% within testing range. The cohesion of the samples with crack development changed slightly with moisture dissipating, while the internal friction angle increased linearly with moisture dissipating. The shearing strength of the cracked soil was mainly affected by the internal friction angle.Conclusion The development of soil cracks in purple soil farmlands has obvious stage characteristics. It has a significant effect on the shearing strength of soil, and it is more obvious when the moisture content is low. The influence of crack development on soil cohesion is greater than that of internal friction angle.
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Keywords:
- Soil bund /
- Soil crack /
- Shearing strength /
- Moisture dissipating /
- Purple soil
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图 1 紫色土坡耕地埂坎土壤裂隙发育过程
Figure 1. Development process of soil cracks on the bunds in purple soil sloping farmlands
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图 2 紫色土坡耕地埂坎裂隙参数变化
Figure 2. Variation of crack parameters of the bunds in purple soil sloping farmlands
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图 3 埂坎土壤抗剪强度随含水率的变化
Figure 3. The variation of soil shearing strength with moisture content in bunds
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图 4 埂坎土壤裂隙参数与抗剪强度散点图
Figure 4. Scatter plot of soil crack parameters and shearing strength in bunds
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图 5 埂坎土壤抗剪强度参数随含水率的变化
Figure 5. The variation of soil shearing strength parameters with moisture content in bunds
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图 6 埂坎土壤裂隙发育过程示意图
Figure 6. The schematic diagram of crack development process in bund soil
表 1 紫色土坡耕地埂坎供试土样概况
Table 1 General situation of soil samples on the bunds in purple soil sloping farmlands
容重
Bulk density
（g cm–3）自由膨胀率
Free expansion rate
（%）总孔隙度
Total porosity
（%）有机质
Organic matter
（g kg–1）颗粒组成 Particles （%） 黏粒
Clay
（< 0.002 mm）粉粒
Silt
（0.002 ~ 0.05 mm）砂粒
Sand
（> 0.05 ~ 2 mm）1.44 ± 0.15 36.33 ± 0.08 42.33 ± 0.03 12.12 ± 0.24 13.89 ± 0.11 81.25 ± 0.05 4.86 ± 0.05 注：表中数据为均值 ± 标准差。 
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表 2 埂坎土壤裂隙参数与抗剪强度相关系数
Table 2 The correlation coefficient between soil crack parameters and soil shearing strength in bunds
项目
Item裂隙面积率
Crack area ratio面积－周长比
Area-perimeter
ratio形状指数
Shape
index分形维数
Fractal
dimension抗剪强度 0.93** 0.92** 0.87** 0.84** 注：**代表显著相关（P < 0.01）。
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表 3 裂隙参数与土壤抗剪强度的相关研究结果
Table 3 Results of study on correlation between crack parameters and soil shearing strength
土样来源
Source of soil
sample试验方法
Test type土壤类型
Soil type试验参数
Test parameter抗剪强度参数
Shearing strength parameter裂隙密度
Crack area ratio
（%）黏聚力衰减率
Rate of cohesion decay
（%）来源
Sourceρd （g cm–3） w （%） c （kPa） φ （°） 边坡 直剪 黄棕壤 1.5 10.0 12.0 29.0 4.9 27.6 汪时机等[9] 工地 直剪 黄壤 1.8 17.0 41.6 12.5 4.9 25.9 李科成等[20] 工地 直剪 黄壤 1.8 21.4 29.2 7.1 4.9 25.2 韦秉旭等[21] 公路 三轴 红壤 1.6 23.0 97.0 6.5 4.9 45.8 陈开圣[22] 工地 直剪 红壤 1.9 16.8 18.9 10.4 4.9 38.8 刘馥铭等[23] 边坡 直剪 红壤 1.5 10.0 761.0 52.0 − 28.0 黄丽华等[24] 埂坎 直剪 紫色土 1.4 10.0 15.8 31.1 4.9 47.6 本研究 注：表中“-”代表无数据，ρd为干密度，w为含水率，c为黏聚力，φ为内摩擦角。
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