Research on Shear Resistance of Rooted Soil under Freeze-Thaw Cycles Based on DEM
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摘要:
为探究冻融循环下草本植物根系土抗剪性能及细观损伤机制，以狼尾草根土复合体为对象，构建了典型的三维根系模型，通过离散元方法模拟水-冰颗粒相变膨胀效应来表征冻融损伤过程，并基于室内试验数据标定了根土复合体三维直接剪切数值模型，系统探究了冻融循环次数、剪切速率以及法向荷载对根土复合体剪切强度、损伤机制和根土复合体抗剪协同作用机制的影响.研究发现：(1)根系的加入可以显著提升土体的抗剪强度，而竖直根系的锚固作用在其中起到了主要作用，须根可进一步增强三维加筋效应；(2)剪切峰值强度和加载速率与法向荷载呈正相关，但二者对冻融损伤造成土体抗剪强度衰减的内在规律影响较小；(3)冻融损伤主要体现在冻融进程中相变产生体积变化破坏试样颗粒粘结，降低剪切过程中根土间作用力，进而削弱其抗剪性能.研究结果揭示了植物根系固土与冻融循环的相互作用机制，为寒区边坡工程的生态加固设计提供了参考依据，特别在极端冻融循环工况下具有重要工程指导价值.
Abstract:To investigate the shear resistance performance and meso-damage mechanisms of herbaceous plant root-soil systems under freeze-thaw cycles, this study focused on wolfsbane root-soil composites. A representative three-dimensional root system model was constructed. The freeze-thaw damage process was characterized by simulating the expansion effect of water-ice particle phase transformation using the discrete element method (DEM). A three-dimensional direct shear numerical model for the root-soil composite was calibrated based on indoor experimental data. The study systematically investigated the influence of freeze-thaw cycle count, shear rate, and normal load on the shear strength, damage mechanisms, and synergistic shear-resistance mechanism of the root-soil composite. The research findings revealed that: (1) The incorporation of roots significantly enhances the shear strength of the soil, with the anchoring effect of vertical roots playing a primary role. Fibrous roots can further augment the three-dimensional reinforcement effect. (2) Loading rate exhibits a positive correlation with both normal load and peak shear strength. However, its impact on the intrinsic pattern of shear strength degradation caused by freeze-thaw damage is relatively minor. (3) Freeze-thaw damage primarily manifests as the deterioration of particle bonding within the specimen, induced by volumetric changes during phase transitions in the freeze-thaw process. This leads to a reduction in interfacial forces between roots and soil during shear, thereby diminishing the soil's shear strength. The results elucidate the interaction mechanism between plant root soil reinforcement and freeze-thaw cycles. They provide a reference basis for the eco-reinforcement design of slope engineering in cold regions, offering significant engineering guidance significance, notably under extreme freeze-thaw scenarios.
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Key words:
- discrete elements /
- root-soil complex /
- freeze-thaw cycle /
- direct shear /
- engineering geology
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图 4 试验与数值剪切应力-位移曲线对比
Fig. 4. Comparison of experimental and numerical shear stress-displacement curves
图 7 数值模拟冻融下剪切峰值强度示意图
Fig. 7. Schematic diagram of peak shear strength under numerical simulation of freeze-thaw
图 8 冻融循环作用后不同剪切速率下峰值强度变化
Fig. 8. Changes in peak strength at different shear rates after freeze-thaw cycles
图 10 冻融循环作用后不同法向荷载下峰值强度变化
Fig. 10. Variation of peak strength under different normal loads after freeze-thaw cycles
图 12 不同冻融次数后根土复合体中微裂隙数量占比
Fig. 12. Percentage of microfractures in root-soil complexes after different freeze-thaw times
图 13 不同冻融次数后两类试样总裂隙数
Fig. 13. Total number of fissures in the two types of specimens after different freeze-thaw times
图 14 各工况下剪切过程产生剪切裂隙情况
Fig. 14. Generation of shear cleavage by shear process under various working conditions
图 15 各工况下剪切过程产生张拉裂隙情况
Fig. 15. Generation of tension cracks by shear process under various working conditions
图 16 各工况下剪切过程产生总裂隙情况
Fig. 16. Total fissure generation by shear process under various operating conditions
图 18 冻融循环下剪切后典型力学参数变化情况
Fig. 18. Changes in typical mechanical parameters after shear under freeze-thaw cycles
图 20 剪切完成时颗粒转角对比
Fig. 20. Comparison of particle corners at the completion of the shear
图 21 冻融循环下剪切过程中根系接触力与倾斜角
Fig. 21. Root contact force and inclination angle during shearing under freeze-thaw cycles
表 1 土的基本物理性质
Table 1. Basic physical properties of soil
材料特性 数值 比重 2.72 塑限(WP, %) 16.5 液限(WL, %) 31.7 塑性指数(Ip) 15.6 最佳含水率(%) 17 最大干密度(kg/m3) 1 790 土样类型 粉质黏土 
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表 2 根系基本特征
Table 2. Basic properties of the root system
根系直径范围(mm) 总长度(mm) 总表面积(cm2) 总体积(cm3) 相对含量(%) 0~0.5 319.11 15.67 0.10 3.90 0.5~1.0 111.21 26.76 0.53 20.40 1.0~1.5 122.65 46.42 1.41 54.40 1.5~2.0 17.65 9.29 0.39 15.00 2.0~2.5 3.54 2.42 0.13 5.10 2.5~3.0 0.45 0.40 0.03 1.20
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表 3 数值模型参数设置
Table 3. Numerical model parameter settings
参数 取值 土体密度(kg/m3) 1 790 土颗粒最大粒径(mm) 2.0 土颗粒最小粒径(mm) 1.6 水密度(kg/m3) 1 000 水颗粒最大粒径(mm) 0.7 水颗粒最小粒径(mm) 0.5 根密度(kg/m3) 450 根半径(mm) 0.5
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表 4 数值模型接触参数设置
Table 4. Numerical model contact parameter settings
颗粒接触 线性刚度(N/m) 平行粘结刚度(N/m) 法向切向刚度比 摩擦系数 颗粒间拉伸强度(kPa) 颗粒间粘聚力(kPa) 土-土 8e6 8e6 4.0 0.35 1.3e2 1.3e2 土-水 2e7 2e7 1.5 0.5 2e5 2e5 土-根 2e7 2e7 1.5 0.6 5e4 5e4 水-水 1e9 1e9 1.5 0.5 2e5 2e5 水-根 1e7 1e7 1.5 0.5 2e5 2e5 根-根 3.5e8 3.5e8 1.5 0.5 3e4 3e4
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表 5 数值模拟试验工况设计表
Table 5. Design of numerical simulation test condition
试验对象 冻融次数 法向荷载(kPa) 加载速率(m/s) 发育须根的根土复合体 0, 1, 3, 5, 10 50 0.01, 0.05, 0.1, 0.5 100 200 300
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