根土相互作用关系对树干振动特性的影响

Effects of root-soil interaction on trunk vibration characteristics

为研究树木在外载荷作用下发生振动时土壤与根系间的力学关系,以北京林业大学苗圃内的4棵3年生毛白杨为研究对象,分别在自然状态、根土摩擦以及固定端约束3种根土相互作用关系下,进行了振动试验并测量了自振频率。分别对应上述3种关系建立了根土刚性连接、根土摩擦和固定端约束3种有限元模型,并通过模态分析得到了模型自振频率。对比实验值与模拟值,探讨了根土间相互作用关系对树木振动特性的影响。结果表明:(1)在3种不同的约束下,树干振动试验所得的自振频率大小依次为:固定端>自然状态>根土摩擦,而且三者的数值差异显著;(2)有限元模型结果中自振频率大小依次为:固定端>根土刚性连接>根土摩擦,与实验结果吻合,说明采用根土刚性连接模型模拟自然状态情况较其他两种模型效果更好;(3)随着外载荷的增大,土壤对树木振动特性的影响也显著增大。

In order to explore the mechanical relationship between roots and soil when trees vibrated under external loads, and then analyze the lodging-resistant mechanism of roots, this study measured the natural frequency of four Chi- nese white poplars grown in nursery of Beijing Forestry University. Trunk vibration tests were conducted in three different circumstances respectively, which include in-situ growth and root-soil friction and fixed end. The root-soil stiffness con- nection model, root-soil friction model and fixed end constrained model had been constructed to simulate three circum- stances mentioned above. After that the natural frequency of the models had been calculated. Based on a comparison be- tween the simulation values and the experimental values, the effect of interaction between roots and soil on vibration properties of trees had been analyzed. The results show that ： （ 1 ） the natural frequency of trees in three different root- soil interaction constrained circumstances had obvious difference, the size order was fixed end 〉 in-situ growth 〉 root- soil friction. （2） the size order of three finite element models was fixed end 〉 root-soil stiffness connection 〉 root-soil friction, it was in accordance with the test result. Root-soil stiffness connection model which was used to simulate trees in-situ was more accurate than other models; （3） Along with the increasing of the external force, the influence of soil on tree vibration properties enhanced gradually.