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EFFECT OF SOIL MOISTURE CONTENT ON SHEAR STRENGTH OF ROOTED SOIL IN LOESS REGIONS OF XINING BASIN
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摘要: 为进一步研究植物根系的固土护坡力学效应，探讨边坡土体含水量对植物根系增强土体抗剪强度的影响，以西宁盆地长岭沟流域作为研究区，选取两种优势灌木植物柠条锦鸡儿(Caragana korshinskii Kom.)、白刺(Nitraria sphaerocarpa Maxim.)和两种优势草本植物芨芨草(Achnatherum splendens(Trin.)Nevski)、细茎冰草(Agropyron trachycaulum Linn. Gaertn.)作为供试种，设置土体含水量分别为6%、10%、14%、18%、22% 5种不同梯度条件，制备根-土复合体和不含根系素土扰动试样，并在室内分别进行直剪试验，分析5种含水量条件下根-土复合体抗剪强度指标的变化规律。试验结果表明：4种草本和灌木植物根系具有显著提高边坡土体抗剪切变形的能力，随着含水量梯度的增加，素土与根-土复合体抗剪切变形能力减弱；当土体含水量相同时，与不含根系素土试样相比，根-土复合体的黏聚力普遍大于素土，而其内摩擦角变化相对较小，其中根-土复合体黏聚力的增长量为1.94~12.17 kPa，增长幅度为34.50% ~360.69%；素土与根-土复合体的黏聚力随土体含水量的增加呈二次多项式函数关系递减，且其内摩擦角亦随着含水量增加而降低，当土体含水量由6%增加至22%时，黏聚力降低幅度为28.50% ~61.78%，内摩擦角降幅为38.73%。本项研究成果对于进一步探讨高寒干旱环境草本和灌木根-土复合体抗剪强度的影响因素，以及利用乡土优势植物开展植被护坡具有重要理论研究价值和实际指导意义。Abstract: This paper aims to deeply investigate the role of vegetation roots in faxing soil and increasing soil strength and probe into the influence of soil moisture content on soil strength. It selects Changlinggou catchment in Xining Basin as the tested site. Four types of local vegetation were chosen as the tested species. They are Caragana korshinskii Kom., Nitraria sphaerocarpa Maxim., Achnatherum splendens(Trin.)Nevski, and Agropyron trachycaulum Linn. Gaertn. Five sets of undisturbed and remolded rooted soil with soil moisture contents increasing from 6% to 22% were prepared for indoor direct shear tests. The results show that all of the vegetation roots possess a capacity of significantly resisting deformation of rooted soil, but as moisture contents increase, the root role in resisting soil deformation is reduced. At the same moisture content, the cohesion of rooted soil is generally larger than that of non-rooted soil. The growth rate of cohesion is 1.94~12.17 kPa and the growth amplitude is 34.50% ~360.69% in comparison to the non-rooted soil. However, the same trend did not occur in the internal friction angle. A binomial function can describe the relation of soil moisture content with its cohesion for all of the soil. Moreover, as the moisture content increases from 6% to 22%, the cohesion declines from 28.50% to 61.78% and the internal friction angle declines by 38.73%. The works possess theoretical and practical significance on further exploring the factors influencing the shear strength of herb and shrub root-soil composite systems, adopting dominant local plants to carry out slope protection, and effectively preventing and controlling regional soil erosion, shallow landslide and other geological disasters.
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Key words:
- Xining Basin /
- Cold-arid environment /
- Soil water content /
- Root-soil composite system /
- Shear strength
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图 1 制取复合体试样所用植物根系与土体试样
a. 植物根系；b. 土体粒径小于0.25 mm素土
Figure 1. Plant roots and soil samples for the preparation of root-soil composite system
图 2 试验区边坡土体的粒径级配累积曲线
Figure 2. Grain size gradation and accumulation curve of slope soil in testing area
图 3 制备完毕的灌木和草本植物根-土复合体试样
a. 柠条锦鸡儿根-土复合体；b. 白刺根-土复合体；c. 芨芨草根-土复合体；d. 细茎冰草根-土复合体
Figure 3. Preparation of root-soil composite system of shrub and herb species
图 4 含水量10%条件下素土和根-土复合体剪应力与剪切位移之间的关系
a. 柠条锦鸡儿根-土复合体; b. 白刺根-土复合体; c. 芨芨草根-土复合体; d. 细茎冰草根-土复合体; e. 素土
Figure 4. The influence of different shear displacement on the shear strength between soil without root and rooted soil under the condition of 10% water content
图 5 不同含水量条件下柠条锦鸡儿根-土复合体剪应力与剪切位移之间的关系
a. 含水量为6%；b. 含水量为10%; c. 含水量为14%；d. 含水量为18%; e. 含水量为22%
Figure 5. The shear displacement connection with shear strength of root-soil composite system of Caragana korshinskii Kom. under different water content
图 6 素土与根-土复合体黏聚力与含水量之间的变化关系
Figure 6. Relationship between cohesion and water content of soil without root and rooted soil
图 7 素土与4种植物根-土复合体内摩擦角与含水量之间的关系
Figure 7. The internal friction angle connection with water content of soil without root and rooted soil
图 8 灌木与草本植物护坡作用示意图(李国荣等，2007；略作改动)
Figure 8. Schematic diagram of shrub and herb slope protection function
表 1 试验区边坡土体物理性质指标试验结果(刘亚斌等，2020)
Table 1. The experiment results of physical properties of slope soil in testing area
深度
/cm平均干密度
/g·cm-3平均含
水量/%液限
WL/%塑限
WP/%液性
指数IL塑性
指数IP土粒组成/% 不均匀
系数Cu土质
类型0.25~0.075 mm 0.075~0.005 mm <0.005 mm 0~100 1.25±0.06 9.12 24.6 17.2 -0.97 7.40 30.10 62.6 7.30 3.90 粉土 
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表 2 试验区素土与4种植物根-土复合体试样黏聚力的增长量和增长幅度计算结果
Table 2. The growth amount and amplitude of cohesion of rooted soil in testing area
试样类型 黏聚力增长量Δc/kPa 黏聚力增长幅度/% ω=6% ω=10% ω=14% ω=18% ω=22% ω=6% ω=10% ω=14% ω=18% ω=22% 素土 — — — — — — — — — — 柠条锦鸡儿根-土复合体 12.17 11.89 12.13 11.61 11.47 146.27 184.63 260.86 305.53 360.69 白刺根-土复合体 9.75 8.63 9.42 8.54 8.01 117.19 134.01 202.58 224.74 251.89 芨芨草根-土复合体 7.30 6.38 6.24 5.87 5.34 87.74 99.07 134.19 154.47 167.92 细茎冰草根-土复合体 2.87 2.78 2.43 2.23 1.94 34.50 43.17 52.26 58.68 61.01
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表 3 试验区素土与4种植物根-土复合体黏聚力值及其与含水量之间的拟合方程
Table 3. The cohesion of soil without root and rooted soil and its fitting equation with water content in testing area
试样类型 黏聚力c/kPa 拟合方程 相关系数R2 ω=6% ω=10% ω=14% ω=18% ω=22% 素土 8.32 6.44 4.65 3.80 3.18 y=12.421 43-0.7705x+0.015 89x2 0.998 28 柠条锦鸡儿根-土复合体 20.49 18.33 16.78 15.41 14.65 y=24.423 79-0.7375x+0.0133x2 0.999 52 白刺根-土复合体 18.07 15.07 14.07 12.34 11.19 y=22.764 04-0.916x+0.017 99x2 0.992 57 芨芨草根-土复合体 15.62 12.82 10.89 9.67 8.52 y=20.417 82-0.923x+0.017 54x2 0.998 01 细茎冰草根-土复合体 11.19 9.22 7.08 6.03 5.12 y=15.549 54-0.8025x+0.014 87x2 0.997 05
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