Yang Ming, Défossez Pauline, Danjon Frédéric, Fourcaud Thierry
Ann Bot. 2014 Sep;114(4):695-709. doi: 10.1093/aob/mcu122.
Windstorms are the major natural hazard affecting European forests, causing tree damage and timber losses. Modelling tree anchorage mechanisms has progressed with advances in plant architectural modelling, but it is still limited in terms of estimation of anchorage strength. This paper aims to provide a new model for root anchorage, including the successive breakage of roots during uprooting.
The model was based on the finite element method. The breakage of individual roots was taken into account using a failure law derived from previous work carried out on fibre metal laminates. Soil mechanical plasticity was considered using the Mohr-Coulomb failure criterion. The mechanical model for roots was implemented in the numerical code ABAQUS using beam elements embedded in a soil block meshed with 3-D solid elements. The model was tested by simulating tree-pulling experiments previously carried out on a tree of Pinus pinaster (maritime pine). Soil mechanical parameters were obtained from laboratory tests. Root system architecture was digitized and imported into ABAQUS while root material properties were estimated from the literature.
Numerical simulations of tree-pulling tests exhibited realistic successive root breakages during uprooting, which could be seen in the resulting response curves. Broken roots could be visually located within the root system at any stage of the simulations. The model allowed estimation of anchorage strength in terms of the critical turning moment and accumulated energy, which were in good agreement with in situ measurements.
This study provides the first model of tree anchorage strength for P. pinaster derived from the mechanical strength of individual roots. The generic nature of the model permits its further application to other tree species and soil conditions.
风暴是影响欧洲森林的主要自然灾害，会造成树木受损和木材损失。随着植物结构建模技术的进步，树木锚固机制的建模也取得了进展，但在锚固强度估算方面仍存在局限性。本文旨在提供一种新的根系锚固模型，包括树木连根拔起过程中根系的连续断裂。
该模型基于有限元法。利用先前对纤维金属层压板所做工作得出的失效定律来考虑单个根系的断裂。采用莫尔 - 库仑破坏准则来考虑土壤的力学塑性。使用嵌入三维实体单元网格划分的土壤块中的梁单元，在数值代码ABAQUS中实现根系的力学模型。通过模拟先前在一株海岸松树上进行的树木拉力试验对该模型进行测试。土壤力学参数通过实验室测试获得。将根系结构数字化并导入ABAQUS，同时根据文献估算根系材料特性。
树木拉力试验的数值模拟显示，在连根拔起过程中出现了符合实际情况的根系连续断裂，这在所得的响应曲线中可以看出。在模拟的任何阶段，都能直观地在根系中找到断裂的根。该模型能够根据临界转向力矩和累积能量估算锚固强度，估算结果与现场测量结果吻合良好。
本研究提供了首个基于单个根系力学强度的海岸松树木锚固强度模型。该模型的通用性使其能够进一步应用于其他树种和土壤条件。
