Currently, the research regarding the effects of plant roots on stabilizing earthen slopes lagged behind engineering practices and the relevant reinforcement mechanism from a microscopic perspective still remains uncertain. In this study, the stability of soil slopes reinforced by the plant roots in three different morphologies (the uniform, the upside-down triangular and the fusiform) was numerically simulated, which was verified by physical rainfall experiments. Then, computational fluid dynamics and discrete element method (CFD-DEM) coupling simulation was adopted to explore the different reinforcement mechanisms of the plant-root systems in different morphologies on the soil slope stability under heavy rainfall. It was disclosed that the roots in a uniform morphology reinforced the slope toe effectively by providing strong shear resistance in the middle and anchoring forces at the end of the root system. The roots in an upside-down triangular morphology strengthened the upper slope by virtue of its wide upper roots extending deeply into the lower soils and hence giving a full play to larger tensile forces. Compared with the previous two root systems, the roots in a fusiform morphology showed the weakest reinforcement effects due to the narrow upper roots and fewer lower roots for anchoring. During the rainfall-induced slope slip failure, the soil particles near the middle-upper part of slope featured faster sliding speed, longer sliding path and larger rolling angle than those closer to the lower slope. The existence of plant roots hindered soil particles from sliding and slowed down the development of slip surface, having the displacement area limited within the rhizosphere zone. The contact forces of roots declined first as the slip surface expanded upward and then increased slowly due to mobilization of the friction between the roots and soil particles. During the rainfall-induced slope failure, the lateral roots toward the slope interior had larger tensile forces; the longest tap-root in the middle of the root system was not always the one having the strongest tensile force, which changed over time.

中文翻译：

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强降雨条件下不同形态植物根系对土坡稳定性的加固机制微观分析

目前，植物根系对土质边坡稳定作用的研究滞后于工程实践，相关的微观加固机理仍不清楚。本研究对均匀、倒三角形和梭形三种不同形态的植物根系加固土坡的稳定性进行了数值模拟，并通过物理降雨实验进行了验证。然后，采用计算流体力学与离散元法（CFD-DEM）耦合模拟，探讨不同形态的植物-根系系统对强降雨条件下土坡稳定性的不同加固机制。研究表明，形态均匀的根系通过在根系中部提供较强的抗剪力和在根系末端提供锚固力，有效地加固了坡脚。根部呈倒三角形形态，其上部根部较宽，深入下部土壤，充分发挥较大的拉力，从而加固了上部斜坡。与前两种根系相比，纺锤形形态的根系由于上部根部较窄，下部根部用于锚定的数量较少，因此表现出最弱的加固效果。在降雨诱发的边坡滑移破坏过程中，靠近边坡中上部的土颗粒比靠近下边坡的土颗粒具有更快的滑动速度、更长的滑动路径和更大的滚动角。植物根系的存在阻碍了土壤颗粒的滑动，减缓了滑面的发育，位移范围仅限于根际区内。随着滑面向上扩展，根系的接触力首先下降，然后由于根系与土壤颗粒之间的摩擦力的动员而缓慢增加。降雨引起的边坡破坏过程中，朝向边坡内部的侧根受到较大的拉力；根系中部最长的主根并不总是具有最强拉力的根，它会随着时间的推移而变化。