CAJ | 학술논문

为深入了解花棒（Hedysarum scoparium）根系在增强土壤抗剪强度中的作用机理，同时减少试验成本和挖掘根系对环境的破坏，该文采用有限元数值模拟的方法研究了宁夏毛乌素沙地5 a生人工种植花棒根系的根截面积比（root area ratio，RAR）和垂直荷载对根-土复合体抗剪强度的影响，并对模拟结果进行了试验验证。研究表明：花棒根-土复合体的抗剪强度与垂直荷载的关系符合摩尔库伦（Mohr–Coulomb）屈服准则，花棒根系对土壤的抗剪强度有显著的提高作用。随RAR的增加，花棒根系表观黏聚力（root apparent cohesion，SR）呈线性增加（R2>0.9）。在相同的RAR下，花棒根-土复合体抗剪强度相对于素土抗剪强度的增长率随垂直荷载的增加逐渐降低，符合对数函数变化规律（R2>0.9）；在相同的垂直荷载下，随RAR的降低，花棒根-土复合体抗剪强度相对于素土抗剪强度的增长率呈线性递减（R2>0.9）；在较低垂直荷载的情况下，花棒根系提高土壤抗剪强度的作用更明显。研究发现与素土相比花棒根-土复合体的剪应力峰值出现较晚，当土壤出现明显塑性变形时，花棒根系的固土能力才能体现出来。数值模拟结果和室内试验结果显示：利用该文所建立的花棒根-土复合体直剪试验的有限元数值模型，模拟计算的根-土复合体抗剪强度与室内试验结果基本一致，相对误差绝对值的平均值1.87%，花棒根-土复合体的直剪试验可以通过该研究所建立的有限元数值模型来模拟。研究结果对于深入了解植物根系加固土壤的作用机理和推进根-土相互作用的数值模拟研究具有重要参考意义。
위심입료해화봉（Hedysarum scoparium）근계재증강토양항전강도중적작용궤리，동시감소시험성본화알굴근계대배경적파배，해문채용유한원수치모의적방법연구료저하모오소사지5 a생인공충식화봉근계적근절면적비（root area ratio，RAR）화수직하재대근-토복합체항전강도적영향，병대모의결과진행료시험험증。연구표명：화봉근-토복합체적항전강도여수직하재적관계부합마이고륜（Mohr–Coulomb）굴복준칙，화봉근계대토양적항전강도유현저적제고작용。수RAR적증가，화봉근계표관점취력（root apparent cohesion，SR）정선성증가（R2>0.9）。재상동적RAR하，화봉근-토복합체항전강도상대우소토항전강도적증장솔수수직하재적증가축점강저，부합대수함수변화규률（R2>0.9）；재상동적수직하재하，수RAR적강저，화봉근-토복합체항전강도상대우소토항전강도적증장솔정선성체감（R2>0.9）；재교저수직하재적정황하，화봉근계제고토양항전강도적작용경명현。연구발현여소토상비화봉근-토복합체적전응력봉치출현교만，당토양출현명현소성변형시，화봉근계적고토능력재능체현출래。수치모의결과화실내시험결과현시：이용해문소건립적화봉근-토복합체직전시험적유한원수치모형，모의계산적근-토복합체항전강도여실내시험결과기본일치，상대오차절대치적평균치1.87%，화봉근-토복합체적직전시험가이통과해연구소건립적유한원수치모형래모의。연구결과대우심입료해식물근계가고토양적작용궤리화추진근-토상호작용적수치모의연구구유중요삼고의의。
Plant roots have considerable impact on the shear properties of soil, but to date the underlying mechanisms have been poorly quantified. In order to understand the fundamental mechanisms of soil reinforcement by Hedysarum scoparium roots and reduce the cost of the testing and relieve the destruction of environment due to digging roots, five-year plant specimens were collected from the Gaoshawo forest field (Northwest China) by in-situ excavation in this study. The shear properties of root-soil composite of Hedysarum scoparium were studied by the finite-element numerical simulation software. The influence of the root area ratio (RAR) and the vertical load on the shear strength of root-soil composite of Hedysarum scoparium was discussed in this study. The laboratory direct shear test was used to prove the reliability of the numerical simulation under the condition of the 7% soil moisture content and the RAR of 0.0034. The results showed that the shear strength of roots-soil composite conformed to the Mohr-Coulomb’s yield criterion and the roots of Hedysarum scoparium could notably enhance the soil shear strength. It was also found that a strong correlation between the RAR and the root apparent cohesion. The root apparent cohesion increased with the increasing of the RAR according to a linear function (R2>0.9). Under the same RAR, the capacity of soil reinforcement by the roots was weakened with the increase of the vertical load, and a logarithmic function (R2>0.9) could be used to describe the relationship between the shear strength growth rate of root-soil composite to pure soil and the vertical load. Under the same vertical load, the growth rate of shear strength of root-soil composite to pure soil decreased linearly with the decreasing of the RAR (R2>0.9). The roots of Hedysarum scoparium played an obvious role to reinforce soil under the low vertical loads. The results of the study indicated that the peak value of the shear stress of root-soil composite of Hedysarum scoparium appeared later compared with that of pure soil. It implied that the root reinforcement did not occur until the significant plastic deformation appeared. Therefore, the roots seemed to have little influence on soil reinforcement for small strains acting on soil-root composite. The numerical simulation results were consistent with the results of laboratory test (the maximum relative error was only 4.26%). It was found that an increase in the vertical load of root-soil composite of Hedysarum scoparium made the contribution of roots to the shear strength increment of root-soil composite decrease. The differences of the cohesion stress and friction angle of root-soil composite of Hedysarum scoparium were only 0.6179 kPa and 0.0039° respectively based on the fitting equation between the vertical load and the shear strength. The fitting equation was developed from the numerical simulation and the laboratory direct shear test results. This paper presented a numerical simulation model capable of simulating the direct shear of root-soil composite of Hedysarum scoparium. The numerical simulation results could serve as the basis and reference for further studies on shear characteristics of root-soil composite.