WU Yihan, ZHU Zhiyuan, ZHENG Lu, BI Yuzhang. 2025: Protective effect and mechanisms of defense pile on bridge pier impacted by granular flows. Journal of Mountain Science, 22(8): 2960-2980. DOI: 10.1007/s11629-024-9412-3
Citation: WU Yihan, ZHU Zhiyuan, ZHENG Lu, BI Yuzhang. 2025: Protective effect and mechanisms of defense pile on bridge pier impacted by granular flows. Journal of Mountain Science, 22(8): 2960-2980. DOI: 10.1007/s11629-024-9412-3

Protective effect and mechanisms of defense pile on bridge pier impacted by granular flows

  • Bridge pier failures from granular flow impacts are common. Installing defense piles upstream is an effective mitigation strategy, yet their protective mechanisms and standardized design guidelines are unclear. This study employed 3D discrete element method to analyze the influence of defense pile size and placement on its performance across 219 scenarios, providing a detailed examination of their protective mechanisms. Results show that optimizing these factors can reduce the maximum impact force on bridge piers by up to 94%. In terms of size, a critical height threshold is identified, beyond which increasing pile height does not enhance protection. This threshold depends on the movement height of granular particles at the slope base. Protection effectiveness varies with pile size: when H ≤ 0.05 h (H is the height of defense piles, h is the height of bridge), protection marginally improves with increasing height and diameter; for 0.05 h < H < 0.15 h, protection strongly correlates with both parameters; for H ≥ 0.15 h, diameter becomes the dominant factor. In terms of placement, an optimal longitudinal distance exists between the defense pile and the bridge pier. The larger the diameter, the greater the optimal longitudinal distance. However, the transverse distance is inversely related to protection effectiveness. Mechanistic analysis shows that defense piles are more effective at redirecting particles to prevent direct collisions with the pier (contributing 100% impact energy reduction before the non-dimensional travel time t* = 7.01 and 63% – 100% afterward) than at reducing particle velocity. This study provides insights into the protective mechanisms of defense piles and informs strategies for optimizing bridge pier protection in granular flow-prone regions.
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