Strain distribution during anchorage failure of Pinus pinaster Ait. at different ages and tree growth response to wind-induced root movement
Strain distribution during anchorage failure of Pinus pinaster Ait. at different ages and tree growth response to wind-induced root movement
复制标题
艾特松锚固破坏过程中的应变分布。
作者：
A. Stokes
对5年生、13年生和17年生的松树(Pinus Pinaster Ait.)以便确定锚固失效模式在树的整个生命周期中如何变化。当树木被侧拉时，用连接在应变指示器上的应变计记录沿侧根的应变。在绞车过程中对根系中的应变进行测量，可以提供有关根在风中移动的信息。机械故障的模式似乎取决于树龄。最年轻的树在绞盘时完全弯曲，但由于树干的可塑性，没有折断。这些13年生的树要么在树的底部(由于嫁接疤痕组织的存在)折断，要么在主根的底部折断。最老的树在自来水根的底部折断了，还听到了断根的声音。树干的应变是5年和13年生树根的两倍，17年生树的压缩根是树干的三倍。在一棵17年生的树上，张力根的应变在35厘米处增加，然后又下降。虽然破坏模式随树体大小的变化而变化，但锚固力与树干直径的3次方成正比，因此破坏随树龄而异的另一个原因必然存在。为了确定侧根中是否存在不同类型的木材对风荷载的响应，在根的不同点上测量了成熟应变，这表明发育中的木材细胞存在机械应力。在只沿风向生长的根中，成熟应变与绞车过程中测得的应变有很高的相关性。因此，树木似乎能够对外部负荷压力做出反应，甚至在根内的局部水平上也是如此。
Winching tests were carried out on 5- 13- and 17-year-old tap rooted Maritime pine (Pinus pinaster Ait.) in order to determine how the mode of anchorage failure changes throughout the life of a tree. As trees were pulled sideways, strain along the lateral roots was recorded using strain gauges attached to a strain indicator. Measurements of strain in the root system, taken during winching, provide information about root movement when loaded by wind. The mode of mechanical failure appeared to depend on tree age. The youngest trees bent over completely during winching, but did not break due to the plasticity of their trunks. The 13-year-old trees either broke at the base of the tree (due to the presence of grafting scar tissue) or at the base of the tap-root. The oldest trees broke at the base of the tap-root and sounds of roots breaking were also heard. Strain was twice as great in the trunk compared to the roots in the 5- and 13-year-old trees and was three times greater in the compression roots of 17-year–old trees compared to that in the trunk. In one 17-year-old tree, strain was found to increase at a distance of 35 cm in tension roots before decreasing again. Although the mode of failure changed with tree size, anchorage strength increased proportionally with the third power of trunk diameter, therefore another reason why failure differs with tree age must exist. In order to determine if different types of wood were being laid down in the lateral roots in response to wind loading, maturation strains, indicating the existence of mechanical stress in developing wood cells, were measured at different points along the roots. A high correlation was found between maturation strain and strain measured during winching, in roots that lay in the wind direction only. Therefore, trees appear to be able to respond to external loading stress, even at a local level within a root.