Defense structures are commonly constructed on the upstream side of bridge piers to mitigate the impact of potential debris-flow events. In this study, field investigations were carried out to obtain the geological conditions and geometric layout of engineering structures on a typical debris-flow site. A two-phase numerical model was adopted to simulate the dynamic processes of the debris flow rushing through a group of defense structures, and the V-shape debris-flow wakes detached from the defense structures were numerically studied. The results show that an oval-shape two-phase flow structure was formed due to the dynamic interaction between two neighboring debris-flow wakes. The shape of this flow structure is related to the viscosity, impact velocity, base fiction and structural arrangement. The corresponding center position and the maximum thickness of this superposed wakes are found to be correlated (nonlinearly or linearly) to the Froude number, Reynolds number, Manning friction number and lateral spacing of the defense structures. The present study improves the understandings toward the effects of the protective structural system on the debris-flow dynamics and can be used to optimize the structural design in debris-flow risk area.

防御结构通常建在桥墩的上游侧，以减轻潜在泥石流事件的影响。本研究通过实地调查，获得典型泥石流场址的地质条件和工程结构几何布局。采用两相数值模型模拟泥石流冲过一组防御结构的动力学过程，对从防御结构脱离的V形泥石流尾流进行数值研究。结果表明，由于两个相邻的泥石流尾流之间的动态相互作用，形成了椭圆形的两相流结构。这种流动结构的形状与粘度、冲击速度、基体摩擦和结构排列有关。发现该叠加尾迹的相应中心位置和最大厚度与弗劳德数、雷诺数、曼宁摩擦数和防御结构的横向间距相关（非线性或线性）。本研究提高了对保护结构系统对泥石流动力学影响的认识，可用于优化泥石流风险区的结构设计。