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Effect of flood defence trees on control of overflow and its threshold breaking condition.

防洪树木对溢流控制的影响及其突破条件

基本信息

批准号：
21860013
负责人：
YAGISAWA Junji
金额：
$ 1.71万
依托单位：
Saitama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Research Activity Start-up
财政年份：
2009
资助国家：
日本
起止时间：
2009 至 2010
项目状态：
已结题

项目摘要

The research was conducted to elucidate the effect of shear stress reduction due to plant and its breaking condition. Firstly, flume experiments were conducted. Porosities of vegetation model were selected 80% and 95%. In these experiments, water depth, velocity and drag force acting on vegetation model were measured. By using obtained experimental data, shear stress acting on slope of embankment model was calculated. Shear stress on slope of embankment model decreased with decreasing porosity. However, when porosity of vegetation model is small (85% porosity case), shear stress at rear side of vegetation model increased drastically. This indicates that to maintain the porosity of vegetation is very important for preventing the levee erosion.On the other hand, for elucidating breaking condition for real tree, tree pulling experiments that simulated flood action were conducted using Salix babylonica and Juglans ailanthifolia, exotic and invasive trees in Japanese rivers. The resulting damage was examined in order to assess the effects of physical tree characteristics and root architecture on the maximum resistive bending moment (M_<max>) for overturning. In situ soil shear strength tests were conducted in order to measure soil strength parameters. Significantly correlated (p<0.05) non-linear relationships were found between M_<max> and tree characteristics, and H*D_<bh>^2 provided the best predictor of the M_<max> within them. Non-linear models were fitted between M_<max> and D_<bh> for each species. The more efficient root architecture to withstand overturning is the heart-root system of S. babylonica, and the plate-root system of J. ailanthifolia is less efficient not with the same breast height diameter but with the same root volume. The average M_<max> of S. babylonica for overturning each species decreased linearly with increasing soil cohesion within the experimental range because root anchoring depth is restricted with increasing the soil cohesion.

本研究旨在阐明植物及其破碎条件对剪切应力降低的影响。首先进行了水槽试验。植被模型的孔隙率选择为80%和95%。在这些实验中，水深，流速和阻力作用在植被模型测量。利用试验数据，计算了路堤模型边坡上的剪应力。路堤模型边坡上的剪应力随孔隙率的减小而减小。而当植被模型孔隙率较小时（85%孔隙率情况），植被模型后侧剪应力急剧增大。另一方面，为了阐明真实的树木的破坏条件，利用日本河流中的外来和入侵树木--垂柳和胡桃楸，进行了模拟洪水作用的拔树实验。由此产生的损害进行了检查，以评估树木的物理特性和根结构的最大抗弯力矩（M_）倾覆的影响<max>。为了测量土的强度参数，进行了原位土抗剪强度试验。M_2与树体性状之间存在显著相关（p<0.05）的非线性关系<max>，其中H* D_^2<bh>是M_2的最佳预测因子<max>。每个物种的M_和D_之间拟合非线性模型<max><bh>。抗倾覆能力较强的根构型是S.相同胸径、相同根体积的臭椿盘根系统效率较低。S<max>.在试验范围内，各树种的倾覆力随土壤粘聚力的增加而线性下降，这是因为根系锚固深度受土壤粘聚力的限制。