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Experimental study on the water blocking effect of tree head-stone in the treatment of pit collapse
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摘要: 河堤窝崩发生后，首先需要确定的是抢护治理方案，减缓窝塘流速，遏制窝塘进一步发展。在诸多抢护治理方案中，树头石方案具有较好的减速促淤效果，但树头高度和抛投间距在以往的设计中都是依经验确定，缺乏理论基础和试验依据。通过制作长江扬中河段指南村窝崩模型，在窝崩口门附近流速模拟相似的基础上，对窝塘内同一高度3种间距的树头石排列型式和同一间距3种高度的树头石进行了试验，用三点法测量了窝塘内12个点的流速、流向。试验结果表明：窝塘内表层流速受惯性影响较大，底层流速受地形影响较大；窝塘内布置不同高度和不同间距的树头石时，平均流速随树头石高度的增加而减小，随树头石间距的减小而减小，窝内流速的减小，意味着泥沙淤积强度的增大；另一方面，树头石高度的增大和间距的减小，都会增加工程的投资成本，研究认为在相对树高为0.15、间距为6 m×6 m时综合效果较佳。Abstract: An effective emergency treatment for the pit collapse is vital to slow down the flow velocity of the pit pond and prevent the further development of the pit pond. The scheme of tree head-stone has been widely used in engineering application owing to its capacity of promoting siltation. The height and the spacing distance of the tree head-stone were generally determined by engineering experience, and these empirical values were short of theoretical and experimental basis. The arrangements of tree head-stone in pit collapse were tested using the physical model at Zhinan village, along the Yangzhong embankment of the Yangtze River. In this study, three heights and three spacing distances were orthogonally combined in the testing scheme, and the flow direction and velocity were measured at 12 locations using the three point method. Based on the analysis of the experimental results, the surface velocity was greatly affected by inertia, and the bottom velocity was dominantly controlled by the topography of riverbed. In comparison of the experiments with different heights and spacing distances, the mean flow velocity increased with the spacing distance of the stone, but decreased with the increasing height of the tree head. The resulting low flow velocity increased the possibility of siltation. Because the investment cost would increase with the height of tree head and the low spacing distance of stone, the best relative height of tree head and the spacing distance of stone were 0.15 and 6 m×6 m, respectively.
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Key words:
- Yangtze River embankment /
- pit collapse treatment /
- tree head-stone /
- mean flow velocity
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图 2 树头石和模型中用的塑料树和塑料草
Figure 2. Tree head-stone and plastic trees and grass for the model
图 4 无工程时窝塘附近表面流场分布(PIV测)
Figure 4. Surface flow field near model without engineering (using Particle Image Velocimetry technology)
图 6 相对树高0.22时按 3 m×3 m间距布置后窝塘内的流速分布
Figure 6. Velocity distribution under 3 m×3 m spacing with the relative tree height of 0.22
图 7 相对树高0.22时不同间距排列下窝内流速比较
Figure 7. Velocity comparison of model measuring points under different spacing arrangements with the relative tree height of 0.22
图 8 树头石密度与相对流速关系
Figure 8. Relationship between density of tree head-stone and water velocity
图 9 6 m×6 m间距排列时不同相对树高下窝内流速比较
Figure 9. Velocity comparison of model measuring points under different relative tree heights with 6 m ×6 m spacing arrangement
图 10 树头石相对高度与相对流速关系
Figure 10. Relationship between relative tree height and water velocity
表 1 模型测点流速验证
Table 1. Verification of velocity of measuring points in physical model
模型 流量/(m3·s−1) 各测点流速/(m·s−1) 1 2 3 4 验证值 28 500 0.678 1.158 0.705 0.750 要求值 0.657 1.098 0.671 0.792 
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