Experiments on shear properties of vetiver root-red clay root-soil composite under different failure modes
Article Text (Baidu Translation)
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摘要: 为探究香根草根系对红黏土剪切特性的影响，选取一年生香根草根-红黏土复合体为研究对象，在获取红黏土和香根草根基本参数的基础上，通过直接剪切试验、单根拉拔试验、界面剪阻试验得到不同破坏模式下根土复合体抗剪强度及剪切特征参数，并进一步分析了根段倾角、土体干密度与含水率影响下的抗剪强度变化规律。研究结果表明：不同法向荷载下的根土复合体的直剪强度均大于素土，当生长方向与受剪方向夹角较小时，土体抗剪强度增幅较大，当根轴与剪切方向平行时，根固效应比二者正交时更好，根系的加入对黏聚力提升的效果显著；抗拔力随拉拔位移的增加而增长，并在3~8 mm位移时出现峰值，其后经历快速和缓慢降低2个阶段，直至根段被完全拔出；拉拔力、界面抗剪强度均与干密度呈正相关性，但当土体含水率约为20%，即最优含水率附近时出现峰值；随着土体干密度的增大，根表与土颗粒之间的黏结得到了增强，同时根土接触面积和摩擦效应也出现同步增长；根土界面抗剪强度、界面黏聚力、界面摩擦因数比均在含水率为20%左右达到最大值；在给定土体密实度水平下，通过调控根系生长环境湿度，可以改善根土摩擦效应和减少根系拉拔破坏。研究成果可为准确评价不同失效模式下根土复合体的抗剪强度提供试验依据，对于根系固土模型中剪切参数的合理选取具有一定参考价值。Abstract: To investigate the influence of vetiver roots on the shear properties of red clay, one-year-old vetiver root-red clay composites were selected as the research object. After obtaining the basic parameters of red clay and vetiver roots, the shear strength and shear characteristic parameters of the root-soil composite under different failure modes were obtained through direct shear tests, single root pullout tests, and interfacial shear resistance tests. Furthermore, the variation laws of shear strength under the influences of root segment inclination angle, soil dry density, and water content were analyzed. The results show that the direct shear strength of the root-soil composite under different normal loads is greater than that of plain soil. When the angle between the root growth direction and the shear direction is smaller, the increase in soil shear strength is larger. When the root axis is parallel to the shear direction, the root reinforcement effect is better than that under orthogonal conditions. The addition of roots shows a significant effect on the improvement of soil cohesion. The pullout force increases with increasing pullout displacement and reaches a peak at a displacement of 3-8 mm, after which two stages of rapid decrease and slow decrease are experienced until the root segment is completely pulled out. Both the pullout force and the interfacial shear strength exhibit positive correlations with soil dry density, but peak values appear when the soil water content is approximately 20%, that is, near the optimum water content. With increasing soil dry density, the bonding between the root surface and soil particles is enhanced, while the root-soil contact area and friction effect increase simultaneously. The interfacial shear strength, interfacial cohesion, and interfacial friction coefficient ratio of the root-soil interface all reach maximum values at a water content of approximately 20%. Under a given level of soil compaction, the root-soil friction effect can be improved and root pullout failure can be reduced by regulating the humidity of the root growth environment. The research results provide experimental evidence for the accurate evaluation of the shear strength of root-soil composites under different failure modes and have reference value for the reasonable selection of shear parameters in root-reinforced soil models.
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Key words:
- road engineering /
- root-soil composite /
- lab test /
- shear property /
- failure mode /
- vetiver /
- red clay
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图 6 根径与抗拉力、抗拉强度的关系
Figure 6. Relationships between root diameter and tensile force or tensile strength
图 12 不同含水率试样的拉拔过程曲线
Figure 12. Pullout process curves of test sample with different water contents
图 13 不同含水率条件下根土界面抗剪强度随根径的变化曲线
Figure 13. Variation curves of root-soil interface shear strength with root diameter under different water contents
图 14 根土界面剪切参数随土体干密度的变化
Figure 14. Variation of shear parameter of root-soil interface with different soil dry density
表 1 红黏土基本物理指标
Table 1. Basic physical indicators of red clay
ω/% ρ/(g·cm-3) ρd, max/(g·cm-3) e wL/% wp/% Ip/% 25 1.67 1.79 1.04 59.8 28.1 31.7 
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表 2 直剪试验方案
Table 2. Test scheme of direct shear test
工况 根段角度 根段长度/mm S A A30 α=30°，β=0° 40 A60 α=60°，β=0° 23 B B90 α=90°，β=0° 20 C C120 α=120°，β=0° 23 C150 α=150°，β=0° 40 D D30 α=30°，β=90° 40 D60 α=60°，β=90° 23
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表 3 拉拔试验方案
Table 3. Scheme of pullout test
ρd/(g·cm-3) K/% ω/% l*/mm 1.34 75 15 60 20 25 30 1.43 80 15 20 25 30 1.52 85 15 20 25 30
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表 4 界面剪阻试验方案
Table 4. Scheme of interface shear resistance test
ρd/(g·cm-3) K/% ω/% σ/kPa 1.34 75 15 25、50、75、100 20 25 30 1.43 80 15 20 25 30 1.52 85 15 20 25 30
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表 5 素土与含根土试样的抗剪强度及强度参数
Table 5. Shear strength and strength parameters of plain and rooted sample
工况 不同法向荷载下的抗剪强度/kPa c/kPa φ/(°) 12.5/kPa 25.0/kPa 50.0/kPa 100.0/kPa S 13.30 17.62 26.53 43.41 9.08 19.00 A30 17.00 21.85 32.98 50.80 12.51 21.17 A60 16.63 20.70 31.81 48.90 12.06 20.43 B90 14.70 20.05 31.63 46.20 11.35 19.71 C120 15.93 20.91 30.38 48.29 11.60 20.23 C150 15.12 20.89 28.73 47.70 10.92 20.13 D30 16.43 21.73 32.79 49.90 12.33 20.88 D60 16.20 20.51 29.57 47.30 11.70 19.60
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表 6 不同干密度及含水率下根土界面抗剪强度
Table 6. Shear strength of root-soil interface under different dry density and water content
ρd/(g·cm-3) ω/% 不同法向荷载下的抗剪强度/kPa 25.0/kPa 50.0/kPa 75.0/kPa 100.0/kPa 1.34 15 12.58 23.27 31.51 41.92 20 15.02 23.75 31.69 42.12 25 13.48 20.52 31.21 37.25 30 8.54 15.29 21.07 28.39 1.43 15 13.79 22.85 33.42 43.08 20 16.07 23.29 34.52 43.52 25 14.59 22.29 32.11 41.08 30 8.64 14.29 21.97 27.29 1.52 15 14.38 25.36 33.79 44.30 20 16.02 26.47 33.82 44.39 25 15.11 22.78 32.43 41.69 30 9.53 15.21 23.18 29.54
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表 7 不同含水率条件下的界面摩擦因数比
Table 7. Interface frictional coefficient ratio under different water contents
ω/% φsr/(°) φ*/(°) Ksr 15 21.80 20.60 1.06 20 20.81 19.20 1.09 25 20.30 18.82 1.08 30 15.64 15.13 1.03
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