桥墩附近冰塞演变与河床局部冲刷相互作用及其机理研究

In cold region, many bridges have been built over rivers. Thus, both hydraulic condition and boundary condition of flow have been changed by the presence of bridge piers. Together with the presence of Ice cover in rivers, sediment transport process and ice accumulation around bridge piers will be intensified. Up to date, local scour and ice accumulation process around bridge piers as well as the interaction between ice accumulation and local scour have been hardly investigated, although numerous research work have been conducted to study local scour process around bridge piers under open flow condition. The impact of ice accumulation on the local scour process around bridge pier has never investigated..The proposed research work will address some important gaps in the scientific literature, including, (a) assessing ice accumulation process of ice jam around bridge pier under condition of movable bed channel; (b) studying the local scour around bridge pier on under condition of ice accumulation; (c) investigating the interaction between local scour and ice accumulation around bridge pier; d) studying the thickness profile of ice accumulation around bridge pier; and (e) analyzing the influence of ice accumulation on the scour-hole range around bridge pier.The proposed research work will consist of follow three parts: experimental study, theoretical analysis and numerical simulation. It will be on the basis of our current research project regarding ice accumulation around bridge pier under condition of fix-bed channel. Research works regarding ice accumulation and local scour process around bridge pier as well as the mechanism of interaction between ice accumulation and local scour process are very important. Results will provide theoretical framework on bridge design and prevention of ice jam flooding in cold region.

随着寒冷地区跨河桥梁的兴建，河道边界条件、水流条件、河床泥沙运动状态和冬季冰塞演变的条件发生了相应变化，桥墩附近产生河床冲刷、冰塞演变和两者的相互作用。明流条件下桥墩局部冲刷国内外相对研究较多，针对桥墩附近冰塞演变与局部冲刷相互作用及其机理的研究几乎未见。. 拟开展桥墩附近冰塞演变与河床局部冲刷相互作用及其机理的研究，包括桥墩附近局部冲刷对冰塞形成和演变的影响、对冰塞演变作用的力学机理、稳封期冰塞体厚度分布的影响以及冰塞演变对桥墩附近局部冲刷深度和范围的影响。拟采用试验研究、理论分析和数值模拟等方法，依托无冲刷条件下冰塞形成演变和冰塞与桥墩相互水力作用特性的研究成果，研究冰期桥墩附近冰塞演变与河床局部冲刷及其相互作用机理，可为高寒地区防凌减灾与桥梁建设提供一定的理论支撑。

寒冷地区跨河桥梁的兴建改变了河道边界条件和水力条件，同时，河床泥沙运动状态和冬季冰塞演变的情况也相应发生变化，桥墩附近局部冲刷、冰塞演变两者之间相互作用。依托无冲刷条件下冰塞形成和演变的研究成果，开展了桥墩附近局部冲刷对冰塞形成和演变的作用机理研究；分析了初始冰塞的形成位置和发展至平衡冰塞所需时间，对比了有、无局部冲刷条件下平衡冰塞厚度和水位增值，形成了不同边界、水流条件下冰塞形成和平衡的判别依据。采用理论分析方法，建立了桥墩局部冲刷对冰塞作用的单元力学模型，研究了桥墩局部冲刷对冰塞作用的力学机理；得到了局部冲刷影响下的冰波波峰厚度和冰波运动速度计算公式，发现桥墩处的输冰能力随冲刷坑深度及冰下水深的增加而减小。进一步地，采用试验研究方法，研究了不同边界、水深、流速、桥墩等条件稳封期冰塞体厚度分布的影响；通过对比有无冲刷条件下试验结果，平衡冰塞厚度随墩径的增大而增大，随弗劳德数的增大而减小，串列桥墩时平衡冰塞厚度随墩间距增大而减小，在弯槽中，桥墩附近凹岸的平衡冰塞厚度大于凸岸。最后，通过对比有无冰塞、不同冰盖糙率、不同床沙条件的试验成果，结合理论分析方法，研究了冰塞演变对桥墩附近局部冲刷深度和范围的影响；发现冰塞演变使桥墩局部冲刷深度、范围与冲刷量更大，冲刷达到平衡所需时间更长，冲刷深度及冲刷范围随着流速增大和墩径增大等呈现上升的趋势，得出了冲刷坑深度随水深、流速的变化规律。研究成果可为高寒地区预防凌洪灾害与桥梁建设管理提供一定的理论支撑。