泥石流冲击桥墩动力相互作用物理模型试验

在我国西部山区地震、地质活跃带,泥石流灾害对位于泥石流沟道、沟口等位置处的桥墩构成重大威胁。如何量化描述泥石流冲击桥墩的动力过程,是泥石流减灾领域拟要解决的一个重要科学问题。以泥石流灾害威胁成兰铁路沿线桥墩的工程背景为基础,依托大型泥石流模拟系统,进行多组室内大比例泥石流冲击桥墩物理模型试验。研究泥石流流速、流深以及流体特征参数与泥石流冲击压力的相关性。试验结果表明:冲击过程主要受到弗汝德数Fr和雷诺数Re两个无量纲数控制,稀性泥石流冲击压力主要控制参数为Fr,而对于黏性泥石流则同时有Fr和Re的影响;不论是对于峰值冲击力还是冲击功率谱,不同类型泥石流差别显著;在相同重度等条件下,稀性泥石流具有更大的冲击能量;此外,各种类型泥石流通过临界Fr线得到了本质上的区分。研究成果将为桥墩抗泥石流冲击结构设计提供技术支持及科学依据。

Physical model experiments of dynamic interaction between debris flow and bridge pier model

The debris flows are recognised as a major threat to bridge piers located in mountainous gullies, especially in the areas of the active seismological and hydrologic region in Southwest China. It is important to build the dynamic evolution model and quantitatively describe the dynamic process of debris flow impacting bridge pier. In this study, all of the large-scale laboratory tests are conducted by using large multi-functional debris-flow simulation system. The main objectives of our experiments are to find the correlation between impacting pressures and variable factors including velocity, flow depth, and dimensionless characteristic parameters of fluid mechanics and to obtain the dynamic behaviour of bridge pier under the impact of debris flow. The experimental results and dimensionless analysis show that the dynamic process is mainly controlled by two dimensionless numbers of Froude number (Fr) and Reynolds number (Re). Generally, the dimensionless impact pressure is the function of Fr for the low-viscosity debris flows, while for the high-viscosity debris flows, it is the function of both Re and Fr. Different types of debris flows present significant differences in both the peak impacting pressure and impacting power spectrum. Under the same bulk density, the low-viscosity debris flow has greater impact energy than that of the high-viscosity debris flow. In addition, various types of debris flows are essentially distinguished by the critical Fr line. To provide technical support and scientific basis, we analysed the impact signals of different types of debris flows and discussed the mechanism of impact model.