根系和裂隙对土体水力和力学特性影响数值模拟

为探究根系和裂隙对土体水力及力学特性的影响，利用有限元软件计算降雨过程中裂隙和根土间隙对渗流场的影响，并以渗流计算结果为基础，分析降雨对根系固土作用的影响，采用分区强度折减法对降雨前后根?土复合体进行直剪试验模拟，同时考虑了侧根倾角的影响。结果表明，裂隙和根土间隙为雨水入渗提供优先通道，降雨影响深度随裂隙深度增加而增加；有根系时降雨影响深度由主根深度决定，侧根倾角对其影响较小，考虑根土间隙影响的降雨影响深度相较于无根系工况增加了93.3%；根系能显著提高土体的抗剪强度，相对于垂直主根方向的不同倾角，侧根增加土体抗剪强度由大至小依次为60o、45o、30o侧根和无根系；雨水入渗降低了土体强度，同时削弱了根系固土作用，使得降雨后根-土复合体抗剪强度大幅降低，是许多植被覆盖边坡仍发生浅层滑动原因之一。

Numerical simulation of the influence of roots and fissures on hydraulic and mechanical characteristics of the soil

To study the effect of fissures and soil-root interstices on hydraulic and mechanical characteristics of the soil, the FEM numerical tools are used to study the influence of fissure and soil-root interstices on the infiltration during the rainfall process. Then the influence of the rainfall on the reinforcement of roots is analyzed. The zonal strength reduction method is applied to simulate the direct shear tests of the root-soil composite before and after the rainfall, considering the impacts of lateral roots’ angles. The results show that the fissures and soil-root interstices become the preferential channels for rainfall infiltration. The depth of rainfall infiltration increases with the depth of fissures. And it is mainly controlled by the vertical depth of the major root, while the influence of the inclination angle of lateral roots is small. The rainfall infiltration depth with root interstices is increased by 93.3% compared with the case without the root in the soil. The root system can significantly improve the shear strength of the soil. The shear strength of the soil with 60° lateral roots is the greatest, followed by the condition with 45°, 30° and without roots. Rainfall infiltration not only reduces the strength of the soil, but also weakens the reinforcement effect of roots. Therefore, the shear strength of soil-root composite system is greatly reduced after the rainfall, resulting in the sliding of the vegetation-covered slopes in a shallow depth.