透水防护体与水沙运动互馈机制及失稳模式研究

The flow-altering devices, represented by the technology of tetrahedral frames,are new developed eco-protection technology which used for protecting the levee in the latest few years. Observations have shown that tetrahedral frames group could change from scouring rate to buffer of silting state by altering the flow characteristics.The stability of countermeasure is important to project.Based on flume experiments and measurement instruments such as ADV, topography measurement instrument and type-B ultrasonic combining theoretical analysis, the water and sediment movement and failure mechanism near the tetrahedral frames layer will be researched. The discriminant index of whole failure mode for the flow-altering devices will be studied by tests of incipient velocity. The interaction mechanisms of water-sediment movement and flow-altering devices and edge failure of devices will be researched by flow characteristics test. Under live-bed conditions, the mechanism and displacement characteristic parameters of flow-altering devices will also be investigated.The achievement of this studies could improve the theories of river dynamics and scour protection,provide technical support for flood control projects and have important significance and essential applied value.

透水型防护措施是近年来发展起来的"亲水"式冲刷防护技术，目前在防护体减速促淤效果及机理方面的成果较多，而对动床条件下防护体附近水沙运动、失稳模式及判别依据的研究较少。透水型防护工程的稳定是其达到防护效果的保证，事关防护工程的成败。本项目以四面六边透水框架为例，利用ADV、自动地形仪和B超仪等多种量测手段，以水槽试验为主，结合理论分析，深入研究透水防护体起动流速，推导起动流速公式，给出透水防护体整体失稳判别指标；研究透水防护体附近水流与泥沙空间变异特性，掌握边界区域床面剪切应力、垂线含沙量分布型式和泥沙扩散系数等的变化规律，阐述防护体与水沙运动互馈机制及边缘失稳机理，揭示沙波条件下透水防护体响应机制和位移特征参数累积效应。研究成果将会丰富河流动力学学科及冲刷防护理论内容，同时也为三峡下游河道防护等防洪工程和长江黄金水道建设提供科学依据。

透水型防护措施是近年来发展起来的"亲水"式冲刷防护技术，目前在防护体减速促淤效果及机理方面的成果较多，而对动床条件下防护体附近水沙运动、失稳模式及判别依据的研究较少。透水型防护工程的稳定是其达到防护效果的保证，事关防护工程的成败。本项目以四面六边透水框架为例，利用ADV和自动地形仪等多种量测手段，以水槽试验为主，结合理论分析，深入研究透水防护体起动流速，推导起动流速公式，给出透水防护体整体失稳判别指标；研究透水防护体附近水沙空间变异特性，掌握边界区域床面剪切应力等的变化规律，阐述防护体与水沙运动互馈机制及边缘失稳机理，揭示沙波条件下透水防护体响应机制和位移特征参数累积效应。研究表明：（1）在不同来流和床面变化情况下，透水防护体主要有整体破坏、边缘调整和埋置下沉3种不同的响应模式，根据推导的滑动和滚动条件下透水防护体起动流速公式计算以及来流流速、与泥沙起动流速三者之间的相互关系，可以作为各模式的判别依据；（2）当透水防护体厚度小于来流水深的四分之一时，防护体起动摩阻流速趋向于一定值，该定值随着透水防护体架空密度的增加而增加，并且同样趋于一定值3.03cm/s；（3）透水防护体上边缘床面淘刷发生在1.5倍的杆件长度位置，在4.0倍杆件长度区域后形成稳定带状减速区域，而下边缘床面淘刷发生在防护体下游1.65~15倍杆件长度的区域；（4）透水防护体埋置最大相对深度与杆件长度呈负相关关系，与相对水深、沙坡相对坡高呈正相关关系。本研究成果将会丰富河流动力学学科及冲刷防护理论内容，同时也为三峡下游长江河道防护等防洪工程和长江黄金水道建设提供技术支撑。