Development of cracks in expansive soil improved by xanthan gum biopolymer
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摘要: 采用既可抑制膨胀土裂隙扩展，又不影响坡面植被生长的黄原胶生物聚合物对膨胀土进行改良，是膨胀土边坡生态防护新思路。对黄原胶改良膨胀土开展室内干湿循环试验，利用数字图像处理技术(PCAS)对裂隙发育的整个过程进行定量分析，探究了黄原胶掺量对膨胀土裂隙形态特征指标的影响规律，并通过扫描电镜(SEM)、X射线衍射(XRD)试验分析了改良前后膨胀土的微观结构与矿物成分的变化，结合膨胀率试验结果探讨了黄原胶对膨胀土的改良机理。研究结果表明，黄原胶的掺入可以有效提高膨胀土的保水性和抗裂性，试样的平均失水速率和裂隙率均随着掺量的增加呈减小趋势；黄原胶能够降低干湿循环效应对膨胀土的影响，将裂隙宽度控制在较小范围内，增湿过程中易闭合；黄原胶主要通过两个方面抑制膨胀土开裂，一方面通过成键和胶结作用与土颗粒形成“桥联”结构，整体增强土体的抗拉强度；另一方面通过填充和成膜作用阻隔水分与土颗粒接触，减小黏土矿物的水化膜厚度。Abstract: The use of xanthan gum biopolymer, which can suppress the expansion of cracks of in expansive soil without affecting the growth of slope vegetation, is a new approach for ecological protection of expansive soil slopes. The indoor wet dry cycle tests are conducted on the xanthan gum-modified expansive soil, and the digital image processing technology is used to quantitatively analyze the entire process of crack development. The influences of xanthan gum content on the characteristic indices of crack morphology in expansive soil are explored, and the changes in microstructure and mineral composition of expansive soil before and after improvement are analyzed through the scanning electron microscopy and X-ray diffraction experiments, The improvement mechanism of xanthan gum on expansive soil is explored based on the results of the expansion rate tests. The research results indicate that the addition of xanthan gum can effectively improve the water retention and crack resistance of expansive soil, and the average water loss rate and crack rate of the sample decrease with the increase of dosage. The Xanthan gum can reduce the impact of wetting-drying cycle on expansive soil, control the crack width within a small range, and make it easy to close during the humidification process. It mainly inhibits the cracking of expansive soil through two aspects. On the one hand, it forms a "bridging" structure with soil particles through bonding and cementation, enhancing the overall tensile strength of the soil. On the other hand, by filling and film-forming, it blocks the contact between water and soil particles, reducing the thickness of the hydration film of clay minerals.
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Keywords:
- road engineering /
- xanthan gum biopolymer /
- wetting-drying cycle /
- crack /
- microstructure
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图 5 裂隙率和含水率的典型变化曲线及相应的裂隙形态
Figure 5. Typical variation curves of crack rate and moisture content and corresponding crack morphologies
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图 6 黄原胶改良膨胀土试样的最终裂隙图像
Figure 6. Final crack images of xanthan gum-modified expansive soil samples
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图 7 裂隙率随干湿循环次数变化曲线
Figure 7. Relationship between crack rate and number of wetting-drying cycles
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图 8 素膨胀土与黄原胶改良膨胀土的裂隙宽度分布情况
Figure 8. Distribution of crack width in expansive soil and xanthan gum-modified expansive soil
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图 9 裂隙最大宽度与干湿循环次数的关系
Figure 9. Relationship between maximum width of crack and number of wetting-drying cycles
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图 10 改良前后膨胀土微观结构对比
Figure 10. Comparison of microstructure of expansive soil before and after improvement
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图 12 不同黄原胶掺量的膨胀土X射线衍射图谱
Figure 12. X-ray diffraction patterns of expansive soil with different amounts of xanthan gum
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图 13 无荷膨胀率与黄原胶掺量的关系
Figure 13. Relationship between free charge expansion rate and xanthan gum content
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图 14 黄原胶抑制膨胀土裂隙发育机理
Figure 14. Mechanism of xanthan gum inhibiting crack development in expansive soil
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图 15 生物聚合物与MICP技术改良土体的相似性
Figure 15. Similarity of soil improved by biopolymer and MICP technology
表 1 膨胀土基本物理性质指标
Table 1 Basic physical properties of expansive soil
土样名称 自由膨胀率/% 塑限/% 液限/% 塑性指数 最大干密度/(g·cm-3) 最优含水率/% 膨胀土 62 27.3 54.5 27.2 1.57 24.65 
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