冰塞与桥墩相互水力作用特性的研究

River ice jams represents an important hydraulic element in temperate and polar environments. An ice jam affects hydrodynamic conditions through changes in both the boundary conditions of rivers and the thermal regime. It causes changes in water level and flow velocity compared to the ice free conditions, Due to their large aggregate thickness and high hydraulic resistance, ice jams cause unusually high water stages and ice flooding. Bridge piers and bridge abutments in rivers cause a decrease in channel width which significantly changes the flow boundary condition. As a consequence, as reported by many researchers, ice jams often initiate in front of bridge piers/abutments. Through extensive literature review, to our knowledge, very few studies have been undertaken to investigate the impacts of bridge piers on river ice jam. Little research work has been conducted to assess the impacts of bridge piers on the formation/accumulation of ice jam, stability of ice jam, increase in water level caused by ice jam, Several existing research work regarding the impacts of bridge piers on ice conveyance under bridge are just special case study. Research work in the vicinity of bridge piers under ice jammed condition has never been explored up to date. The proposed research will lay a foundation for being a systematic study regarding the hydrodynamics around bridge piers under ice jammed condition, including, (a) formation of ice jam in front of bridge piers, and stability of ice jam in front of bridge piers, (b) accumulation of ice jam in front of bridge piers, (c) variation in water level and discharge caused by ice jam in front of bridge piers, (d) impacts of bridge piers on ice transport under ice jam. Experimental study and combined methods including theoretical analysis, numerical simulation will be conduct cutting-edge study regarding these topics. Research results will lay a foundation for bridge design in cold region, and definitely benefit scientific and engineering community, since riverbed scour around bridge piers under ice jammed condition has been identified as an important issue with potentially catastrophic consequences such as bridge failure.

冰塞是北方寒冷地区河流冬季凌洪灾害的主要诱因，而跨河渠桥梁及其墩台的存在改变了河道中原有的冰塞水力特性，提高了河道中形成冰塞的可能性。围绕冰塞的形成演变，国内外展开了大量的研究工作，但是考虑桥墩对冰塞影响的研究却不多见。从国内外文献检索看，桥墩对冰塞形成、冰塞稳定性、冰塞堆积与壅水、冰塞下过流等方面影响的研究较为少见，开河期桥墩过冰能力方面的研究均针对特定的工程实践开展，其结论不具备普适性；有关冰塞下桥墩冲刷方面的研究则仅有初步涉及。 拟全面开展冰塞与桥墩相互水力作用特性的研究，包括桥墩对冰塞形成、冰塞稳定性、冰塞堆积与壅水、冰塞下过流能力、以及开河期河道过冰等方面的影响。研究拟定以试验研究方法为主，结合采用理论分析、数值模拟等方法，依托无桥墩条件下冰塞形成演变的研究，研究冰塞与桥墩相互水力作用特性的影响关系与规律，为高寒地区防凌与跨河桥梁的建设提供一定的理论支撑。

基于模型试验，研究了桥墩对冰塞堆积演变的影响，通过观察有无桥墩条件下冰塞堆积现象、分析各影响因素对冰塞堆积演变过程的试验数据，给出了桥墩影响下冰塞能否形成的临界判定条件。.基于力学分析的方法，采用平衡冰塞理论，建立冰塞单元力学平衡方程，得到了桥墩影响下冰塞稳定性判别公式，研究所提出的桥墩影响下冰塞稳定性判别公式计算得到的结果和实测资料吻合较好，可为桥墩影响下冰塞的稳定性判别提供理论支撑。.基于模型试验对桥墩影响下的临界流凌密度进行了研究，得到了桥墩条件下临界流凌密度计算公式，并利用试验结果对临界流凌密度计算公式进行验证，结果显示计算得到的临界流凌密度与试验值较为接近，补充一定的天然河道原型观测资料后，对该临界流凌密度计算公式中的参数予以率定，可为天然河道是否封河提供有效的预测。.对桥墩墩型影响下平衡冰塞水位及周围冰塞厚度分布进行了试验研究，与无桥墩冰塞状况以及有桥墩明流状况下水位增值进行对比分析，给出了考虑桥墩墩型影响下的平衡冰塞水位计算表达式。.通过桥墩影响下的S型弯槽冰塞堆积试验，研究桥墩存在及桥墩位置不同对S型弯槽段冰塞水位以及冰厚变化的影响，将试验结果与无桥墩试验及180°弯槽试验进行对比，对水位、冰厚变化特点进行分析，给出了考虑桥墩影响的冰塞水位计算表达式。.对比Beltaos一维冰塞厚度计算公式，基于静态平衡冰塞理论，得到了稳封期冰塞厚度横向分布计算公式，计算得到的结果在整体趋势上与原型观测实测结果比较一致，能够较好的预测冰塞厚度沿横断面的分布。并基于马斯京根法，对冰期河槽调蓄进行分析，分析了冰厚与河槽调蓄作用的关系。.数值模拟了冰盖下桥墩周围的水流结构、基于DEM模型对开河期桥墩对河道过冰能力的影响进行了数值模拟，模拟结果与实测资料吻合较好，可为研究墩台构筑物与冰塞相互水力作用提供支撑。