Thickness effect on crack evolution of expansive soil
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摘要: 膨胀土的裂隙开展受到许多因素的影响,包括自身的土体性质,环境状况,边界条件、土体尺寸等。厚度对膨胀土等黏性土体的开裂规律具有重要的影响,为了探究这种重要因素在膨胀土失水收缩开裂过程中的具体影响规律,试验设置了4个具有不同厚度的大直径圆形泥浆试样。运用图像处理技术,通过记录试样的裂隙演化过程及质量的变化,定量分析裂隙面积分形维数、长度分形维数等指标随含水率下降的动态变化关系。试验结果发现：①厚度对膨胀土失水收缩开裂及裂隙扩展过程有明显影响,厚度较小的试样其裂隙发育充分,裂隙密集细长而纹理丰富；厚度较大的试样裂隙发育单一,裂隙宽大而边界效应明显,通过提出厚度和试样直径的比值,可以初步预估试样的裂隙发育情况；②裂隙面积分形维数受厚度的影响较小,而裂隙长度分形维数受厚度的影响较大,结合两者可以有效地对裂隙形态及分布进行表征,裂隙最终的长度分形维数一般在1～1.5,而面积分形维数基本维持在1.6～1.7。此外,结合土体开裂的张拉破坏理论以及试样的收缩蒸发情况,对厚度影响下的土体开裂差异进行了理论分析,进一步探究了裂隙的扩展规律。Abstract: The crack development of expansive soil is affected by many factors, including soil properties, environmental conditions, boundary conditions and soil sizes. Crack evolution is greatly influenced by thickness. In order to explore the specific influence rules of the thickess in the whole process of water loss shrinkage and cracking of expansive soil, four large-diameter circular mud samples with different thicknesses are prepared in the experiment. With the help of image processing technology, the dynamic change relationship of the basic crack indexes with the decrease of water content are quantitatively analyzed by recording the evolution process of cracks in the samples. The experimental results show that the process of water loss shrinkage and crack expansion of expansive soil are significantly affected by the thickness. The crack of the sample with smaller thickness is fully developed, and it is long and thin. However, the sample with larger thickness has a single wide crack and is affected by obvious boundary effect. The development of the cracks is preliminarily estimated by the ratio of thickness to diameter. In addition, the morphology and distribution of the cracks can be characterized effectively by combining the fractal dimensions of area and length. The fractal dimension of crack length is generally about 1~1.5, while the surface integral dimension is basically maintained at 1.6~1.7. Moreover, based on the tensile failure theory of soil cracking and the shrinkage and evaporation of the samples, the difference of soil cracking affected by the thickness is theoretically analyzed, and the expansion rules of cracks are further explored.
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Keywords:
- expansive soil /
- thickness effect /
- crack evolution /
- fractal dimension /
- quantification
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图 5 裂隙分形维数随含水率的变化关系
Figure 5. Relationship between fractal dimension of cracks and water content
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图 6 不同厚度土体的收缩及开裂演化示意图
Figure 6. Shrinkage and crack evolution of soils with different thicknesses
表 1 试样的主要参数
Table 1 Main parameters of samples
试样编号 直径/mm 厚度/mm 初始含水率/% 环境温度/℃ S1 400 10 60 30 S2 400 20 60 30 S3 400 35 60 30 S4 400 50 60 30 
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表 2 Dha-Df经验拟合参数
Table 2 Empirical fitting parameters of Dha-Df
编号 B C R2 S1 0.411±0.006 1.977±0.008 0.998 S2 0.388 ± 0.005 1.926 ± 0.006 0.998 S3 0.388±0.005 1.904 ± 0.005 0.999 S4 0.352± 0.004 1.854 ± 0.005 0.999
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表 3 Dhl-Rlp经验拟合参数
Table 3 Empirically fitting parameters of Dhl-Rlp
编号 B C R2 S1 0.478±0.008 0.980 ± 0.007 0.995 S2 0.430 ± 0.015 1.012 ± 0.010 0.982 S3 0.459 ± 0.023 0.998 ± 0.014 0.951 S4 0.489 ± 0.030 1.023 ± 0.009 0.936
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