Objective]In order to explore the vulnerable root parts under the axial tension and radial bending force.[Method]The roots of 3 4 year-old Caragana korshinskii Kom.,Salix psammophila C.Wang et Chang Y. Yang,Hippophae rhamnoides Linn.and Artemisia sphaerocephala Krasch.were used as the trial materials,the anti-tension force and anti-fracture force of lateral-root branches and adjacent upper straight roots of the four species were measured with TY 8000 in vigorous growing seasons.[Result]The results showed that both of the anti-tension force and the anti-fracture force were positively correlated with the diameter of roots and followed a power function, and both the anti-tension strength and the anti-fracture strength were negatively correlated with the root diameter and followed a power function.The anti-tension strength of lateral-roots was lower than the anti-tension strength of adjacent straight roots.The anti-fracture strength of lateral-roots was lower than the anti-fracture strength of adja-cent straight roots.The anti-tension strength of lateral-roots and adjacent straight roots of the four species followed the sequence of C.korshinskii (23.70 ±3.97 and 28.02 ±4.40 MPa) >S.psammophila (14.86 ±1 .28 and 20.33 ±1 .76 MPa) >H.rhamnoides (10.60 ±2.40 and 15.86 ±3.90 MPa) >A.sphaerocephala (5.07 ±1 .25 and 8.80 ±1 .74 MPa).The anti-fracture strength of lateral-roots and adjacent straight roots of the four species followed the sequence of C.korshinskii (33.66 ±7.74 and 47.06 ±4.41 MPa) > S.psammophila (17.31 ±1 .91 and 27.54 ±3.82 MPa) >H.rhamnoides (3.97 ±1 .23 and 8.75 ±1 .70 MPa) > A.spha-erocephala (2.18 ±0.39 and 6.15 ±1 .01 MPa).[Conclusion]The lateral-root branches were easier to be damaged than adjacent upper straight roots.What the predictive values of FEMand DEMmodels are slightly high-er than the measured value was caused by the following two fields besides other scholars’interpretation.(1 )the lateral root branches were neglected,the lateral root branches were weak points in contributes to soil reinforce-ment.(2)The FEM and DEM models assumed all roots were members which were subjected to tension along the axial direction.When the root-soil composites were sheared,some roots were subjected to the axial tension and some roots were subjected to the radial tension,or the anti-fracture force was lower than the anti-tension strength, The FEM and DEM Models overestimated the soil preservation ability.%[目的]为探讨根系在轴向拉力和径向折力下的易损部位。[方法]以34 a 的柠条、沙柳、沙棘和白沙蒿为研究对象，采用 TY8000伺服控制材料试验机测定4种植物侧根分支处和相邻直根的抗拉力与抗折力。[结果]表明：在14 mm 根径范围内，4种植物侧根分支处和相邻直根的抗拉力、抗折力均与直径呈幂函数正相关，抗拉强度、抗折强度均与直径呈幂函数负相关；同径级时，每种植物单根的抗拉强度和抗折强度均表现为侧根分支处小于相邻直根，4种植物侧根分支处和相邻直根的抗拉强度为柠条（（23．70±3．97）、（28．02±4．40）MPa）＞沙柳（（14．86±1．28）、（20．33±1．76）MPa）＞沙棘（（10．60±2．40）、（15．86±3．90）MPa）＞白沙蒿（（5．07±1．25）、（8．80±1．74）MPa），侧根分支处和相邻直根的抗折强度为：柠条（（33．66±7．74）、（47．06±4．41）MPa）＞沙柳（（17．31±1．91）、（27．54±3．82）MPa）＞沙棘（（3．97±1．23）、（8．75±1．70）MPa）＞白沙蒿（（2．18±0．39）、（6．15±1．01）MPa）。[结论]无论受轴向拉力还是径向折力，4种植物根系易损部位均为侧根分支处。造成垂直根模型（WWM）和纤维束模型（FBM）预测根系固土能力偏高的补充原因为：（1）模型根系全部计入直根的抗拉力，忽略了侧根分支处，而侧根分支处是根系固土的薄弱点。（2）模型假设所有根系为轴向受拉的杆件。实际根土复合体发生剪切时，根可能承受轴向拉力，也可能承受径向折力。对于抗折强度小于抗拉强度的植物，模型必然高估根的实际固土能力。
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